Elective Single Embryo Transfer: an update to UK Best Practice Guidelines

Abstract

A significant number of multiple pregnancies and births worldwide continue to occur following treatment with Assisted Reproductive Technologies (ARTs). Whilst efforts have been made to increase the proportion of elective single embryo transfer (eSET) cycles, the multiple pregnancy rate or MPR remains at a level that most consider unacceptable given the associated clinical risks to mothers and babies, and the additional costs associated with neonatal care of premature and low birth weight babies. Northern Europe, Australia and Japan have continued to lead the way in the adoption of eSET. Randomised controlled trials or RCTs, meta-analyses and economic analyses support the implementation of an eSET policy, particularly in light of recent advances in ARTs. This paper provides a review of current evidence and an update to the eSET guidelines first published by Cutting et al. (2008) intended to assist ART clinics in the implementation of an effective eSET policy.

Keywords::

• Elective single embryo transfer (eSET)
• multiple pregnancy
• ART
• IVF
• ICSI
• ACE
• BFS
• guidelines

Introduction

In 2009, the Human Fertilisation and Embryology Authority (HFEA) introduced a policy to encourage fertility centres to adopt elective single embryo transfer (eSET) into routine use (HFEA, 2008). This policy required a phased reduction in the multiple birth rate (MBR) from 24 % in 2009, 20 % in 2010, 15 % in 2011, to 10 % in 2012 and thereafter. Initially these targets formed a license condition, but in early 2014 a legal challenge to the HFEA by a UK-licensed fertility centre resulted in the removal of the license condition for all centres (HFEA, 2013). Despite this, the HFEA, the Association of Clinical Embryologists (ACE), the British Fertility Society (BFS) and other stakeholder professional organisations remain fully supportive of the ‘One at a Time’ project supporting eSET and committed to the current 10 % MBR target.

The most recent HFEA trends and figures report (HFEA, 2014) revealed that clinics continue to replace two embryos in the majority of fresh or frozen IVF or ICSI procedures (51.0 % down from 56 % in 2012) with 27.0 % (up from 22.2 % in 2011) receiving eSET. An examination of the annual HFEA data published from 2008 to 2013 reveals an encouraging and sustained trend in reduction of multiple pregnancy rate (MPR) from 26.6 % in 2008 to 16.3 % in 2013. During this time period, the gradual improvement in live birth rate (LBR) from IVF and ICSI treatment, which has been observed since 1994, remained unaffected. What is clearly evident is that although an on-going downward trend in MBR has been observed, further adjustments to clinical practice must still be made if the 10 % recommended target is to be achieved whilst maintaining the LBR.

The message from Europe is clear: countries such as Sweden, Finland and Belgium have clearly demonstrated that a MBR of less than 10 % is achievable. Sweden continues to report the highest percentage of SET at 69.9 %. In 2010, Kallen et al. (2010b) examined trends in delivery and neonatal outcome from the Swedish National Heath Register dataset spanning over 25 years. The study included in excess of 25,000 women receiving IVF treatment over the 5-year period following the introduction of eSET and showed that the risk of neonatal death and morbidity was significantly reduced.

When the first edition of the ACE/BFS guidelines was published (Cutting et al., 2008), many of the Northern European countries had implemented eSET, but only Belgium and Sweden had legislation underpinning it. In 2010, Turkey introduced new legislation mandating SET in women less than 35 years of age in the first or second cycle of treatment and limiting clinics to the transfer of two embryos in the third or subsequent treatment cycles and in women over the age of 35 years (Kultursay et al., 2015). Since the implementation of this policy, preliminary results reported from a small multi-centre study have shown a significant reduction in MPR, with a modest downward trend in clinical pregnancy rate (CPR) from 39.9 % to 34.5 %, although this was not statistically significant (Kutlu et al., 2011).

In 2010 the provincial government of Quebec introduced eSET legislation with the aim of performing SET in every treatment cycle (Bissonnette et al., 2011). The legislation states that multiple embryos can only be transferred in cases where it is justified by the treating physician and on a case-by-case basis. In the first 3 months of the programme, 5 centres performed 1353 IVF cycles with an overall CPR of 32 % per embryo transfer (compared with 43 % prior to the policy being introduced), with 50 % of transfers using eSET. During the same time period, the MPR was reduced from 25.6 % to 3.7 %. Prior to this legislative change, eSET was performed in only 1.6 % of treatment cycles. The fact that central funding was allocated to this project by the provincial health programme must be recognised as a major contributing factor to the successful implementation of the policy in such a short period of time. Velez et al. (2013) showed that the initiative in Quebec reaffirmed the policy of ‘1 plus 1 should equal 2’, with cumulative pregnancy rates from the sequential transfer of one fresh followed by one frozen embryo close to equalling that obtained with the transfer of two fresh embryos together.

In the USA only 1 % of fresh transfers prior to 2002 were eSET, with a modest increasing trend to 5.6 % overall in 2010, with a 9.6 % eSET rate and a 32.4 % twin rate in the < 35 age group. However, in 2012 the Practice Committee of the Society for Assisted Reproductive Technology and Practice Committee of the American Society for Reproductive Medicine published eSET guidance for patient selection (ASRM, 2012). These guidelines concluded that eSET should be promoted and offered to patients with a good prognosis, and to recipients of embryos from donated eggs and that eSET must be applied in association with an effective embryo cryopreservation programme. The most recent data from 2013 now show a more than doubling of eSET in the good prognosis < 35 age group to 22.5 %, and a modest reduction in the twin rate to 28.3 % (SART, 2013).

In 2011, Maheshwari et al. (2011) assessed global variation in the uptake of a SET policy (Table I). They reported that it was not possible to distinguish eSET from non-elective SET from national ART reports but that in over 31 countries there had been a gradual increase in the rate of SET. They suggested that public funding, availability of effective cryopreservation, and national legislation remained the main contributory factors in the establishment of effective SET policy. Whilst legislation in the UK has defined targets the worldwide picture is very variable. Few countries have specific legislation, some have guidance, whist other countries still endorse double embryo transfer (DET). There does however seem to be consensus that embryo quality and age should be taken into account during the decision process (Table I).

Table I. Summary of Global legislation in relation to eSET (adapted from Maheshwari et al., 2011).

Country	Legislation
Australia	No legislation; eSET advised < 35 on first fresh cycle. No more than 2 advised < 40
Austria	Legislation restricts the number of eggs which can be used in IVF. All fertilised embryos must be transferred
Belgium	Legislation; < 36 first cycle must have eSET
Canada	No overall legislation only guidelines suggesting eSET in patient < 35 years in a first or second cycle and consider eSET in patients 36 &37 with good prognosis. Quebec introduced legislation in 2010 which states every cycle should be eSET unless there are suboptimal conditions and clinical justification is given
Denmark	No legislation
Estonia	Max of 3 can be transferred
Finland	No legislation
France	Restricted to DET. If more than 2 clinical justification required
Germany	Legislation restricts the number of eggs which can be used in IVF. All fertilised embryos must be transferred
Greece	No legislation; recommended up to 3 embryos transferred for women up to age of 40 and up to 4 > 40.
Hungary	State regulation limits number to transfer to 3 except in exceptional circumstances when up to 4 can be transferred
India	Guidelines: Max of 3 can be transferred
Italy	Law restricts number of eggs which can be fertilised, all resulting embryos must be replaced
Japan	Recommendation by Japanese Society of Obs and Gynae; max 2 embryos since 2008
Luxemburg	No legislation
Netherlands	No legislation
New Zealand	Guidance related to funding. If publically funded < 35, first or second cycle eSET. No more than 2 embryos (fresh or frozen) < 40.
Norway	No legislation
Portugal	Law contains general addict that multiple embryos should be avoided if possible
Sweden	State legislation states in principle only 1 embryo should be replaced apart from in exceptional circumstances
Switzerland	Legislation restricts the number of eggs which can be used in IVF. All fertilised embryos must be transferred
Turkey	Legislation in March 2010 favouring eSET - limits < 35 to eSET and > 35 to DET.
USA	No overall legislation. Guidelines (ASRM, 2013a) suggest eSET should be offered to patients < 35 and no more than 2 embryos should be transferred. Patients 37–39 no more than 2 cleavage embryos in favourable prognosis patients or if blastocyst transfer. If using cleavage stage transfer in poor prognosis no more than 3 embryos should be replaced. No more than 3 embryos cleavage or 2 blastocysts in patients 38–40 years with favourable prognosis. Other patients in this group no more than 4 cleavage embryos or 3 blastocysts transferred. In patients 41–42 no more than 5 cleavage stage embryos or 3 blastocysts. In patients with 2 or more previous failed cycles one additional embryo can be transferred in each age category. No limit on patients over 43 years old In donor cycles if the donor is < 35 eSET should be strongly recommended

Key: eSET = elective single embryo transfer; DET = Double Embryo Transfer.

Aim

The aim of this guideline review is to provide updated evidence-based guidance, to assist UK fertility centres in the implementation of effective eSET policy with the intention of reducing MPR, whilst not discounting the patients’ right to choice and autonomy. The revised guideline remains highly supportive of the ‘One at a Time’ initiative in the UK, which continues to encourage the practice of eSET.

Scope

The guideline revision will address the need for eSET, patient and embryo selection, superovulation practices, cryopreservation strategies, the role of the HFEA and cost implications.

Levels of Evidence

The hierarchy of evidence and system for grading the strength of the evidence used in this paper are outlined in Table II, as developed by the National Institute for Health and Care Excellence (NICE).

Table II. NICE hierarchy of evidence, and grading the strength of the evidence.

	Hierarchy of evidence
1a	Systematic review and meta-analysis of randomised controlled trials (RCTs)
1b	At least one randomised controlled trial
2a	At least one well-designed controlled study without randomisation
2b	At least one other type of well-designed quasi-experimental study
3	Well-designed non-experimental descriptive studies, such as comparative studies, correlation studies or case studies
4	Expert committee reports or opinions and/or clinical experience of respected authorities

	Grade strength of evidence
A	Requires at least one RCT as part of a body of literature of overall good quality and consistency addressing the specific recommendations. (Evidence levels 1a, 1b)
B	Requires the availability of well-controlled clinical studies but no randomised clinical trials on the topics of recommendation. (Evidence levels 2a, 2b, 3)
C	Requires evidence obtained from expert committee reports of opinions and/or clinical experiences of respected authorities. Indicates an absence of directly applicable clinical studies of good quality. (Evidence level 4)
GPP	Good practice point

Safety

The safety of IVF procedures will be a major consideration throughout. IVF as an intervention occurs at a point in early human development when the embryo is uniquely vulnerable, due to the complete reorganisation of the genome and epigenome immediately after fertilisation. There is general appreciation now that the peri-conceptional environment can influence long-term programming of health in offspring, via largely epigenetic mechanisms (Watkins et al., 2010; Lucas, 2013). This concern is consistent with the long-standing observation that IVF singleton babies are at increased risk of low birth weight (Hansen et al., 2002). With respect to technologies used in selection of embryos for eSET consideration should be given to the potential risk of the technology, set against the accepted benefit of reducing the incidence of multiple pregnancies (see above). The impact of ART and environmental stresses on embryo development and long-term disease is a priority area for research.

Recommendations – Safety

1. Further research is required (a) to validate the efficacy of eSET policies and (b) confirm the long-term safety of the culture and cryopreservation processes that constitute such policies. (C)

Is there still a role for DET?

Results from randomised controlled trials (RCTs) comparing eSET with DET clearly show that the chance of live birth is reduced, unless eSET is combined with an effective programme for the transfer of a subsequent frozen embryo (Lukassen et al., 2005; van Montfoort et al., 2006; Moustafa et al., 2008). This supports the earlier study by Thurin et al., (2004) which reported that the LBR following eSET was significantly reduced compared with DET. However, the cumulative LBR following subsequent replacement of a single frozen embryo in the eSET group was equivalent to the DET group (39 % vs. 43 %). A Cochrane Database System Review has supported these findings (Pandian et al., 2009). More recently, McLernon et al., (2010) published a meta-analysis of 8 RCTs of cleavage-stage eSET versus DET, 5 of which had been published in peer-reviewed journals. This showed a cumulative LBR from 2 eSET (fresh + frozen) cycles with day 2/3 transfer slightly but not statistically significantly lower than that from a single DET cycle (38 % vs 42 %). In addition, statistical modelling of large treatment cycle datasets including the HFEA register has shown that SET would yield about a one-third lower LBR relative to DET, for any embryo transfer (Roberts et al., 2011). However, this difference in LBR can be mitigated by patient and treatment cycle selection, resulting in an increased LBR with sequential eSET, compared with DET, with both fresh and frozen embryo transfers (FETs). Thus, it is undeniable that when combined with an effective cryopreservation programme eSET can yield cumulative success rates that at least match, and may exceed, those from DET (Roberts et al., 2009; 2010b). Given the strength of the accumulating evidence in favour of a well-constructed eSET programme, why should DET still be considered, given the attendant risk of twin pregnancies?

Whilst cumulative cycles with cryopreservation maintain success rates, it is important to consider that this strategy requires multiple cycles and adds an emotional, physical and financial cost to purchasers, either through state funding or (depending on the costing models) patients. Interviews and focus groups conducted with patients undertaking fertility treatment continue to indicate a clear patient preference for twins despite the potential to maintain overall LBR with an eSET strategy (Leese & Denton, 2010; Roberts et al., 2010b). It is therefore vital when considering eSET that clinics ensure the needs of patients are taken into account and that patient preference is not seen as irrational. However, this must be considered in context with the short- and longer-term consequences of avoidable multiple pregnancy and birth. In particular, the desire for patients to have more than one child should be taken into consideration and eSET policies need to allow funding for the transfer of all embryos of transferrable quality, regardless of earlier outcome, if eSET is not to be disadvantageous in this respect.

Secondly, the extended treatment duration in a complete eSET programme may be particularly disadvantageous to older women whose fertility is declining rapidly. Although the evidence suggests that oocyte aneuploidy is the biggest limiting factor in older women, there is also some decline in uterine receptivity (Legro et al., 1995; Stolwijk et al., 1997; Toner et al., 2002; Roberts et al., 2010a). More significantly, repeat egg collections following failure will occur at later ages in an eSET programme, reducing the chances of a successful outcome. This could potentially be mitigated by offering multiple oocyte retrievals or ORs followed by cryopreservation and eSET.

Finally, although the economic costs from a total health service perspective are reduced with eSET (Scotland et al., 2011), this is not true of the direct costs to fertility service providers, or to patients in privately funded treatments.

Selection of patients for DET

Despite the evidence in favour of eSET it is likely that DET will remain part of clinical practice in the UK for the foreseeable future and the question arising is for which patients should DET still be considered. The available evidence suggests that the relative chance of twins is similar for all patients regardless of the usual prognostic factors (Roberts et al., 2010b) with no specific risk factors for twinning, other than embryo quality, being identified. This of course means that the absolute chance of twins is greatest in patients with the best prognosis. In an extensive analysis of the UK HFEA register data, Lawlor and Nelson (2012) concluded that the transfer of three or more embryos at any age should be avoided and that the decision to transfer one or two embryos should be based on prognostic indicators, such as age.

Thus there is, at the time of writing, no clear high-quality evidence for selection of patients for inclusion in an eSET or DET strategy and there are no clear predictors of the likelihood of twins other than stage of embryo development at transfer, and embryo quality. Selection is therefore based on local or anecdotal evidence or a pragmatic financial decision to include those patients most likely to have twins because they are most likely to become pregnant following treatment.

A number of very similar policies for selecting patients for DET have been suggested, which essentially target eSET at those with the best prognosis and therefore reduce the overall twin rate, whilst allowing DET for the poor prognosis patients to maintain their single transfer success rate. In the NICE (2013) guidelines, several factors were recommended which should be considered when determining an individual patient's suitability for eSET. These include maternal age, obstetric and gynaecological history, previous treatment history, ovarian response or reserve, number of embryos created and quality of embryos or blastocysts available for transfer, and cryopreservation. For women under the age of 37 years undertaking their first treatment cycle, the NICE (2013) guidelines advocate eSET. These guidelines largely support the eSET algorithm proposed by Cutting et al. (2008), although they are not specific in terms of the day on which embryo transfer should be performed other than to recommend eSET in circumstances where at least one top-quality blastocyst has developed. The NICE guidelines propose additional recommendations for women in the age ranges of 37–39 and 40–42 years (Table III).

Table III. NICE (2013) Guidelines – Embryo transfer strategy summary table (including fresh & frozen embryos).

Attempt	< 37		37–39		40–42
First Cycle	SET		> 1 Top Quality Available SET	No Top Quality Available Consider DET	Consider DET
Second Cycle	> 1 Top Quality Available SET	No Top Quality Available Consider DET	> 1 Top Quality Available SET	No Top Quality Available Consider DET	*
Third Cycle	No more than 2 embryos		No more than 2 embryos		*

Key: *NICE only recommend a single treatment cycle in women > 40 years of age; SET = Single Embryo Transfer; DET = Double Embryo Transfer.

The relationship between LBR and maternal age is well established (Dessolle et al., 2011; Sifer et al., 2011). In the eSET algorithm published by Cutting et al., (2008), it was recommended that eSET should be routinely applied to patients < 37 years of age. However, a recent report has challenged whether eSET should be restricted solely to younger women. Niinimaki et al., (2013) examined whether eSET for older women between 40 and 44 years could be feasible. This retrospective cohort study appears to be the first to show such a large number of older women consenting for eSET: 42 % of the study population. In fresh cycles, the CPRs were 23.5 % and 19.5 % in the eSET and DET group, respectively, with LBRs of 22.7 % and 13.3 %, respectively (P = 0.002). This study was limited by an inability to compare the two groups directly as the suitability for eSET had been individually assessed by a clinician and not randomised. These findings were challenged by Gleicher (2013), who in addition to questioning the rationale for eSET in older women with reduced prognosis questioned the ‘irrational attraction of eSET’. He commented on the ethics of urging older women to reduce their immediate pregnancy chances and suggested that under most circumstances women of advanced age cannot be considered to have a favourable prognosis. Gleicher highlighted the point that overall, the risk associated with a twin pregnancy (one live birth event) compared with two singleton pregnancies (two separate live birth events) becomes reduced.

A retrospective analysis of the outcome and feasibility of eSET in the first and second transfers was reported by Gremeau et al. (2012). The study showed that from a patient group of 783 couples embarking on a first cycle of IVF or ICSI treatment, the on-going pregnancy and cumulative delivery rates from eSET and DET cycles did not differ significantly (30.9 % and 34.6 %, respectively) with 67.6 % of the transfers being eSET. For the second treatment attempt, the eSET rate dropped to 16.9 % suggesting that eSET is less well accepted by patients for their second attempt, although it should be noted that patient acceptability and clinicians’ advice were not measured independently.

eSET has also been shown to yield a good LBR in oocyte donation programmes. A retrospective study which examined delivery rates before and after the implementation of an eSET policy showed a significant reduction in the twin rate, with no impact on the delivery rate (although the study was not powered to examine this) (Soderstrom-Anttila et al., 2003). This observation was supported by another retrospective study, which suggested that when three embryos are available and eSET is performed, the cumulative LBR is not compromised (Clua et al., 2012). Following these studies, NICE (2013) recommended using an embryo transfer strategy based on the age of the oocyte donor.

Recommendations – Selection of patients for DET

1. There should be a continued focus on minimising MBRs from IVF treatment by utilising an effective, dynamic eSET strategy. (GPP)

2. In situations where embryo quality is poor, clinics should consider the transfer of two embryos. An effective eSET policy should accommodate this. (B)

3. Centres should audit eSET rates, selection criteria, and MBRs and where their dataset is robust, consider adjusting their eSET algorithm in line with their results on at least an annual basis, focussing on good practice rather than small numbers of multiple births above or below a target rate. (GPP)

Superovulation strategies

Traditionally, stimulation protocols have induced pituitary downregulation with a gonadotrophin-releasing hormone (GnRH) agonist followed by gonadotrophin stimulation, or the use of a GnRH antagonist to block the luteinising hormone (LH) surge during the stimulatory phase. A Cochrane review of GnRH antagonists in assisted reproduction (Al-Inany & Aboulghar, 2002) and a more recent update (Al-Inany et al., 2011) suggest that overall the antagonist protocol gave a 1.5 % lower LBR and 2 % lower CPR compared with the agonist protocol. However GnRH antagonist use is associated with a lower risk of ovarian hyperstimulation syndrome (OHSS) compared with GnRH agonist (Mathur & Tan, 2014). The need for safety is paramount and the rationale for ‘aggressive’ stimulation protocols should be questioned in an effort to reduce OHSS and in association with an effective eSET strategy to reduce the incidence of multiple pregnancies. Heijnen et al. (2007) showed that three mild stimulation protocols are as affective as two conventional stimulations in terms of outcome. Baart et al. (2009) described how different ovarian stimulation regimens can affect oocyte and embryo quality.

Recommendations – Superovulation strategies

1. Maximising oocyte and embryo quality is an essential part of an effective eSET strategy; a focus should remain on optimising superovulation regimens. (A)

Selection of embryos or blastocysts for eSET

It is generally accepted that robust embryo selection is a key element in the implementation of an effective eSET programme. This has resulted in increased pressure and expectation on Clinical Embryologists to ensure that the embryo with the best potential to deliver a healthy live birth is selected for transfer. Significant progress has been made in recent years with the various techniques employed for embryo selection.

Morphological oocyte, embryo and blastocyst assessment

a) Oocyte assessment

In predicting embryo quality and implantation potential, it is wise to consider the assessment and quality of oocytes as predictors of embryo competence. However, historically there has been conflict in the literature as to the reliability of these observations, particularly during ICSI. Serhal et al. (1997) suggested that anomalies including granularity and the presence of cytoplasmic inclusions such as vacuoles, smooth endoplasmic reticulum clustering, and refractile bodies had a negative impact on embryo implantation rates. In contrast, Balaban et al. (1998) suggested the exact opposite: that oocyte morphology had no direct effect on fertilisation rate, embryo quality and implantation rate following ICSI. More recently, the Istanbul consensus on embryo assessment (ALPHA, 2011) published evidence suggesting oocyte assessment anomalies should be sub-divided into (i) intra-cytoplasmic (incorporations, refractile bodies, dense central granulation, vacuoles and aggregation of smooth endoplasmic reticulum); and (ii) extra-cytoplasmic dymorphisms (first polar body morphology, perivitelline space size and granularity, discolouration, zona pellucida defects, and shape anomalies). ALPHA (2011) also concluded that ‘giant’ oocytes and oocytes with smooth endoplasmic clusters should be selected against because of their likely abnormal genetic constitution and association with early foetal loss and imprinting disorders, respectively (Otsuki et al., 2004; Ebner, 2008).

b) Pronuclear (PN) assessment

Assessment of pronuclear (PN) morphology is based on observations of features seen in zygotes 16–18 hours post-fertilisation. Grading systems were developed to assess the number, position, size and alignment of the nucleolar precursor bodies (NPB) in each embryo. Zygotes which showed pronuclei of similar size centrally located, containing NPB of equal size and number aligned at the pronuclear interface, were considered to have a good PN score and thus a good prognosis (Scott et al., 2000; Machtinger & Racowsky, 2013). However, the relationship between PN score and embryo quality has not yet been fully established. Some early studies reported good correlation between the PN score and embryo development (Scott et al., 2000; Rienzi et al., 2002; Nagy et al., 2003) but more recent studies have questioned the validity of this form of assessment to predict embryo competency (James et al., 2006; Nicoli et al., 2007; Ahmad et al., 2008). A possible explanation for this conflicting data might be the highly dynamic nature of PN formation. With such rapid changes occurring within short periods of time, early assessments can change rapidly and may therefore be misleading. This has been demonstrated using time-lapse imaging (Montag et al., 2011). A retrospective review by Nicoli et al. (2013) concluded that PN evaluation was only effective if embryo transfer is performed on day one of embryo culture.

c) Cleavage stage embryo assessment

Indicators of embryo development including cell number, evenness of size, and incidence of fragmentation have formed the basis of embryo assessment since the inception of our scientific discipline. More recently, parameters such as multi-nucleation of blastomeres and uneven cell division have enhanced such assessments, which can be performed at the cleavage stage of embryo development.

Cleavage rate

There is a considerable body of evidence suggesting that delayed or rapid embryo cleavage rate has a negative impact on implantation (Edwards et al., 1980; Van Royen et al., 1999; Desai et al., 2000; Roberts et al., 2010a). Two studies have suggested embryos that complete their first cleavage to the 2-cell stage between 25 and 27 hours post-insemination show increased implantation potential (Wharf et al., 2003; Giorgetti et al., 2007). However, further recent data from a multi-centre prospective study has re-assessed the effect of early cleavage on embryo quality, implantation and LBR (de los Santos et al., 2014). This study examined 700 embryo transfers and over 1000 early-stage embryos and showed that for conventional embryo culture and morphological evaluations, the assessment of early cleavage was not considered a valuable selection tool to improve embryo implantation. The Istanbul consensus on embryo assessment (ALPHA, 2011) states that the single most important indicator of embryo viability is the timely occurrence of cell divisions (Balaban & Magli, 2011) as summarised in Table IV. This suggests that embryos that cleave more slowly than the expected rate have reduced implantation potential and those that cleave too rapidly are more likely to be abnormal and have a reduced implantation potential. This has been confirmed by large-scale analysis of UK data (Roberts et al., 2010a).

Table IV. Timing of observation of fertilised oocytes and embryos and expected stage of development at each time point (ALPHA, 2011).

Type of Observation	Timing (hours PI)	Expected Stage of Development
Fertilisation Check	17 ± 1	Pronuclear Stage
Syngamy Check	23 ± 1	50 % in syngamy (up to 20 % at 2-cell stage)
Early Cleavage Check	26 ± 1 post ICSI 28 ± 1 post IVF	2-cell stage
Day 2 Embryo Assessment	44 ± 1	4-cell stage
Day 3 Embryo Assessment	68 ± 1	8-cell stage
Day 4 Embryo Assessment	92 ± 2	Morula
Day 5 Embryo Assessment	116 ± 2	Blastocyst

Key: PI = Post Insemination

Fragmentation

A fragment is defined as an anuclear, membrane-bound extracellular cytoplasmic structure (ALPHA, 2011). Johansson et al. (2003) defined fragments as cells that were < 45 μm in diameter for Day 2 embryos and < 40 μm for Day 3 embryos. The negative effect of increased fragmentation on embryo implantation potential is well established (Alikani et al., 2008). Furthermore, the type and distribution of fragmentation may be related to implantation potential. Large fragments were found to be detrimental whilst small or scattered fragments did not have as much impact (Rienzi, 2005). However, fragments can be transient or migratory and can disappear or be reabsorbed during normal embryo development. For this reason, identification and evaluation of specific fragment patterns may not reflect the embryo's viability as part of a time-specific embryo assessment (Antezak & Van Blerkom, 1999). Fragmentation levels of less than 10 % appear to have negligible impact on implantation (Van Royen et al., 2001).

Cell size

For embryos at the 2-, 4- and 8-cell stages, it is expected that the blastomeres should be of equal size and shape. When blastomere size varies by more than 20 %, reduced implantation potential is observed due to an increased incidence of aneuploidy and multi-nucleation (Plachot et al., 1998; Hardarson et al. 2001; Van Royen et al., 2003).

Multi-nucleation

An embryo can be considered multinucleate when it contains at least one cell that has more than one interphase nucleus (Balaban & Magli, 2011). There is considerable evidence to show that the presence of multi-nucleation correlates with chromosomal abnormalities, uneven cell size and division and lower implantation, pregnancy and LBRs (Hardarson et al., 2001; Van Royen et al., 2003). This is supported by a recent retrospective cohort analysis, which showed that when multi-nucleation is present on Day 2 of development in at least one blastomere, there is an associated increase in the rate of aneuploidy even when a sibling blastomere is biopsied which showed no signs of multi-nucleation (Ambroggio et al., 2011). There are certain factors which are known to affect the rate of multi-nucleation such as the type of culture medium (Winston et al., 1991) and temperature fluctuations (Pickering et al., 1990), the impact of which should be kept to a minimum by good laboratory process control. The optimal stage to assess for this parameter is on day 2, but evaluation does not always confirm multi-nucleation, since the nuclei are only visible during the interphase stage and could potentially be missed (Rienzi, 2005). Time-lapse technology will serve to evaluate further the impact of multi-nucleation as evidence is published on the incidence and outcome of previously undetected multi-nucleated embryos.

Blastocyst assessment and transfer

Advances in embryo culture media and incubation systems have enabled the reliable extended culture of embryos to the blastocyst stage of development, 5 or 6 days following insemination. This allows embryologists flexibility in deciding when to perform the embryo transfer and theoretically should provide certain advantages over the transfer of cleavage-stage embryos. According to the ASRM, (2013b) committee opinion on blastocyst culture, these advantages include:

• A higher implantation rate;

• The opportunity to select the most viable embryo;

• The potential decrease in the number of embryos transferred; and

• Better temporal synchronisation between embryo and endometrium.

However, the potential downsides to blastocyst transfer can include the increased risk of couples not having a transfer when the procedure is applied in unselected patients having fewer embryos available for cryopreservation (Glujovsky et al., 2012). In addition, there are concerns that blastocyst culture results in an increased risk in monozygotic twinning (MZT), including monochorionic and monoamniotic twinning, which are extremely high-risk pregnancies (Vitthala et al., 2009; Chang et al., 2009). This reported increase in MZT does not occur in all blastocyst transfer programmes (Moayeri et al., 2007; Papanikolaou et al., 2010); however, a notable recent analysis of a large number of cycles on the Society for Assisted Reproductive Technologies (SART) database confirmed the association between blastocyst transfer and increased incidence of MZT (Luke et al., 2014). The causal factors are as of yet unknown and couples should be counselled about the possible increased risk of MZT in each particular clinic of blastocyst, compared with cleavage-stage embryo transfer. Counselling should include the advice that MZT carries greatly increased risks compared with dizygotic twinning and not just a higher incidence of twins. In addition, recent reports from national data registries in the US, Canada and Sweden show that babies born from blastocyst transfer are at significantly increased risk of pre-term and very pre-term birth (< 32 weeks) (Kallen et al., 2010b). The underlying cause of this phenomenon is unknown, but may include altered allocation of cells to the placenta in blastocysts developing in vitro. A meta-analysis of these studies (Maheshwari et al., 2013) was not able to control for confounders, but patients should be counselled about the possible risk of pre- and very pre-term birth from blastocyst transfer. There is good evidence in animal models that embryos in prolonged culture are at risk of growth disorders such as Large Offspring Syndrome in sheep and cattle (Young et al., 1998) that arise from epigenetic disorders, with some data also available from human ART (Kallen et al., 2010a; Park et al., 2011). But again, the evidence on this is incomplete and requires further high-quality prospective studies.

There does however appear to be consistent evidence to suggest that in good prognosis populations (defined by such factors as age, number of previous cycles, ovarian response and number and size of follicles at hCG trigger), there is an increased likelihood of live birth per embryo transfer after the transfer of fresh blastocysts compared with cleavage-stage embryos (Gardner et al., 1998; Papanikolaou et al., 2005; Papanikolaou et al., 2006; Glujovsky et al., 2012), particularly when there are supernumerary blastocysts available for cryopreservation (Mullin et al., 2012). However the most recent Cochrane meta-analysis concluded that when both early cleavage and blastocyst stage embryo freezing are taken into account, early cleavage stage transfer results in a higher cumulative pregnancy rate compared with blastocyst transfer (Glujovsky et al., 2012). It should be noted that this evidence was based on studies in which blastocysts were cryopreserved using controlled rate freezing rather than vitrification and this is an area which should be the subject of future review.

Recommendations – Selection of blastocysts for eSET

1. Where blastocyst transfer is performed, clinics should review their eSET data and criteria for extended embryo culture regularly. (GPP)

2. Prospective studies are required to determine the impact of embryo culture to the blastocyst stage on MZT, pre-term birth and associated epigenetic changes and on why MZT appears to be more prevalent in some clinics. (B)

3. Patients should be counselled that current best evidence indicates that blastocyst stage transfer may result in a successful outcome sooner, but with some specific increased risks, and may ultimately lead to a reduction in the overall chance of success. (A)

There are many studies that outline the importance of morphological grading of blastocysts as a predictor of outcome (Gardner et al., 2000; Balaban et al., 2000; Goto et al., 2011; Heitmann et al., 2013). Blastocysts are usually assessed using a 3-part grading scheme which was first suggested by Gardner and Schoolcraft (1999) based on the degree of blastocyst expansion and characteristics of the inner cell mass (ICM) and trophectoderm (TE). More recently, there has been a focus on the particular importance of the TE with its grading correlating more closely with implantation and live birth than that of the ICM (Ahlstrom et al., 2011; Hill et al., 2013).

Following the Istanbul consensus on embryo grading (ALPHA, 2011), it was agreed that an optimal embryo at this developmental stage would be a fully expanded blastocyst with an ICM which is prominent and easily discernible, and consisting of many cells with the cells compacted tightly adhered together, and with a TE that comprises many cells forming a cohesive, even epithelium.

Standardising grading of embryos and blastocysts

The previous ACE/BFS guidelines for practice on eSET (Cutting et al., 2008) suggested a basic grading scheme which has been adopted both by the National External Quality Assurance Scheme or NEQAS embryo grading scheme and by NICE in the 2013 Fertility Guideline Review. The three components described in the grading scheme have been evaluated as predictors of pregnancy and it has been shown that embryo growth rate and fragmentation are by far the strongest predictors of pregnancy potential and that after including these, blastomere evenness did not improve the efficacy of the model to predict pregnancy further (Stylianou et al., 2012). However, it is important to take account of the subjective nature of morphological evaluation and that a laboratory should therefore have a robust approach to external and internal quality assurance (Bjorndahl et al., 2002).

The use of time-lapse imaging for embryo and blastocyst selection

Since the inception of IVF, the universally accepted method to select an embryo or embryos for transfer was via a manual morphological assessment. However, in recent years technological advances have allowed the integration of cameras into incubators to allow time-lapse embryo imaging of the process of morphometric evaluation in real time. This technology enables embryos to be cultured undisturbed, without the need for removal from the incubator for observation, allowing remote monitoring of development by serial image capture (Lemmen et al., 2008). There are many publications (the vast majority of which report on retrospective analyses), which suggest a benefit of morphometric evaluation for selection and de-selection of embryos at key stages in their development (see Aparicio et al., 2013; Bolton et al., 2015) as well as the benefit of having an undisturbed embryo incubation environment. However, Armstrong et al., (2015) has recently published a critical appraisal of the design of time-lapse studies concluding they do not provide robust evidence in favour of time-lapse incubation as an undisturbed culture environment or as an embryo selection algorithm. They also point out the risks of introducing technology without critical appraisal.

Until recently, there had been no evidence based on randomised trials to support the use of time-lapse systems. Rubio et al. (2014) then described the findings of the first randomised controlled prospective study into the efficacy of time-lapse technology. The study, based on 843 cycles, indicated that while the use of time lapse microcopy combined with time-lapse embryo selection algorithm did not result in a statistically significant increase in the pregnancy rate (61.6 % vs. 56.3 %), the implantation rate was increased and early pregnancy loss was reduced (16.6 % vs. 25.8 %). This is without doubt an area where further high-quality large-scale prospective clinical trials are urgently required.

Current evidence does not discriminate between the effects of undisturbed culture and improved embryo selection afforded by time-lapse incubation systems. More recently there has been a focus on evaluating characteristics that are negative predictors for developmental competence and therefore allow the de-selection of embryos (Montag et al., 2013). Negative predictors include direct cleavage from 1 cell to 3 cells, uneven blastomeres at the 2-cell stage and multi-nucleation at the 4-cell stage. Rubio et al. (2012) reported significantly lower implantation rates when embryos exhibited abnormal cleavage patterns. Combined with the work-developing eSET algorithms the information gained from the early cleavage observations could be used to select embryos on day 3 of culture, negating the need for blastocyst culture as a tool for selection (Hashimoto et al., 2012).

Whilst the studies to date show promise that time-lapse parameters have the potential to improve embryo selection beyond standard morphology, incorporation into routine practice will require the development of robust selection algorithms. It is not yet established whether a single algorithm would be appropriate for all centres or for all treatment types. Thus, the algorithms proposed have been based on surrogate endpoints (development to blastocyst stage) or on subsets of pregnancy outcome data where the embryo outcomes are known (all or none of the transferred embryos develop, which represents a biased approach) or restricted to ICSI cycles. With the exception of the work of Herrero et al. (2013), all such studies have been far too small to enable robust algorithm development and validation: when the datasets produced include 20 or more parameters, datasets with more than 400 successful and unsuccessful outcomes are needed, and larger numbers still will be required to establish reliable thresholds.

From data currently available it appears likely that the use of time-lapse technology may facilitate the de-selection of embryos (Bolton et al., 2015). It is also clear that before firm conclusions can be drawn on the benefits of time-lapse technology there is an urgent need for further well-designed large-scale, independent, multi-centre studies with unselected patients to develop and validate selection criteria, followed by RCTs to demonstrate their clinical utility (Bolton et al., 2015). In addition, cost–benefit analyses should be performed to ascertain if benefits attributable to time-lapse incubation systems justify the significant costs involved in the procurement and implementation of the appropriate technology.

Recommendations – Use of time-lapse technology

1. Centres with the resources to support time-lapse morphometric analysis may use this information to improve their eSET algorithm. (GPP)

2. Technological advances including time-lapse imaging and morphometric assessment show promise as embryo selection and de-selection tools, but further high-quality prospective studies are required to develop and validate robust algorithms, followed by RCTs to demonstrate their role in an eSET strategy. (C)

Non-invasive testing of embryo viability

The correlation between metabolic activity and embryo viability was first reported by Renard et al. (1980) in a study that looked at glucose uptake in advanced bovine blastocysts. Since then several studies have reported the use of metabolic, metabolomic, proteomic, genomic and transcriptomic markers as predictors of embryo viability (Leese & Barton, 1984; Van den Bergh et al., 2001; Gardner et al., 2001; Leese, 2002; Brison et al., 2004; 2007; Leese, 2012; Bolton et al., 2015).

Recent papers by Gardner and Wale (2013) and Bolton et al., (2015) have reviewed the analysis of metabolism as a means of selecting viable embryos for transfer particularly with a view to replacing a single embryo. These papers review the data on amino acid turnover along with carbohydrate utilisation and suggest that there are distinct patterns of amino acid utilisation between viable and non-viable blastocysts as initially reported by Houghton et al., (2002) and Brison et al., (2004). Amino acid profiling has an established scientific basis (Brison et al., 2004) but is yet to find a place in routine clinical practice. Refinements of the high-performance liquid chromatography (HPLC) technology to reduce the time it takes to carry out the amino acid profiling may make the process more efficient and attractive for clinical use. Gardner and Wale (2013) have shown that glucose consumption provides a further potential biomarker of the capacity of an embryo to give rise to a pregnancy. Raman and near-infrared spectroscopy have been used to analyse culture medium to examine metabolic profiles (the overall technique is known as ‘metabolomics’) of viable and non-viable embryos (Brison et al., 2007; Seli et al., 2007). However a prospective RCT of a method based on infrared spectroscopy failed to show an improvement in CPR (Hardarson et al., 2012). Other studies have utilised different technologies to assess the metabolomic profile of culture media including proton nuclear magnetic resonance (¹H NMR) spectroscopy (Seli et al., 2008). Respiration rates, in terms of oxygen consumption of oocytes and embryos, have been measured (Scott et al., 2008) and related to embryo viability (Lopes et al., 2007). However, as with the other non-invasive markers discussed, such measurements have yet to find a place in the IVF clinic.

Despite this, selection of the healthiest embryo for eSET is paramount and although not yet available for routine clinical use, these approaches show considerable promise. Further research and prospective trials are required to develop and validate these methods and translate them into clinical practice (Bolton et al., 2015)

Recommendations – Non-invasive testing of embryo viability

1. Further development and evaluation is required of the effectiveness of selecting embryos based on metabolic or related traits. (C)

Pre-implantation genetic diagnosis and screening

In cases where an individual or couple have a known risk of any resultant child being born with or developing a serious debilitating genetic disorder, the process of pre-implantation genetic diagnosis (PGD) can be applied to reduce this risk and ensure that embryos with the best implantation potential are selected for treatment. The procedure has obvious benefits and is not contested by most ART practitioners. However, the use of pre-implantation genetic screening (PGS) has to be one of the most controversial of all the developments in assisted reproduction over the last few years. For more than 10 years, PGS was performed at the cleavage stage of embryo development using Fluorescent in situ hybridization (FISH) yet was shown not to increase the live birth rate (Mastenbroek et al., 2011, Mastenbroek, 2013). This conclusion was supported by the European Society of Human Reproduction and Embryology or ESHRE PGD Consortium who issued a position paper suggesting that there is no improvement in LBRs in patients with advanced maternal age (Harper et al., 2010). In 2008, an ASRM Practice Committee paper suggested that not only did PGS not improve LBRs in older women but also did not improve LBRs in couples experiencing implantation failure or recurrent pregnancy loss (ASRM 2008a).

PGS technology has developed very rapidly since these early papers were published with testing now ranging from polar body biopsy (Magli et al., 2011) to TE biopsy (McArthur et al., 2008). Improved screening techniques have seen successful validation of array comparative genomic hybridisation or aCGH for PGS (Magli et al., 2011; Geraedts et al., 2011; Gutiérrez-Mateo et al., 2011; Mamas et al., 2012) for comprehensive chromosome analysis of embryos. In a rapidly changing science, perhaps the most recent advance in PGS technology has been the development of next-generation sequencing or NGS (Yin et al., 2013; Wells et al., 2014).

Several RCTs have been published, mainly applying PGS to good prognosis patients (Yang et al., 2012; Scott et al., 2013; Rubio et al., 2013; Foreman et al., 2013). Before widespread use of this procedure for embryo selection, it needs to be determined which patients would benefit (Bolton et al., 2015).

Assisted hatching

A committee opinion for ASRM in 2008 did not support the universal application of assisted hatching (AH) in all IVF cycles but did support, at that time, the use of AH in those with two or more failed cycles of treatment, when the woman was aged over 38 years (ASRM, 2008b). A Cochrane review in 2012 including 31 RCTs showed that the CPR in women who underwent AH was marginally improved but the ‘take home baby rate’ was not significantly different (Carney et al., 2012). In addition AH increases the rate of MZT (Hershlag et al., 1999; Schieve et al., 2000; Luke et al., 2014), a finding that needs to be taken into consideration when applying an eSET strategy, particularly when considering the increased incidence of MZT associated with blastocyst transfer (Knopman et al., 2014).

Cryopreservation strategies

Whilst the original ACE/BFS eSET guideline (Cutting et al., 2008) focussed on fresh embryo transfer the importance of implementing an effective strategy incorporating serial SET of cryopreserved embryos should not be underestimated. Cryopreservation is a well-established, routine component of a typical IVF cycle. An effective cryo-programme is essential to maximise the cumulative pregnancy rates, which can be achieved with eSET, irrespective of the day of fresh transfer (Glujovsky et al., 2012).

Several authors have compared outcomes of eSET and DET frozen embryo replacement cycles. For example, Yanaihara et al. (2008) published data from 470 patients receiving vitrified blastocysts transferred in either SET or DET procedures. The results showed similar CPRs for both groups, with a significant reduction in the incidence of ectopic pregnancy in the SET group and a significant increase in twinning in the DET group. Ishihara et al. (2011) supported the use of frozen–thawed blastocyst transfer in reducing the risk of ectopic pregnancy. There is however conflicting evidence on the use of eSET in frozen cycles based on pregnancy outcome in the initial fresh cycle. For example, El-Toukhy et al. (2003) demonstrated a two-fold increase in implantation rate and an increased CPR from the transfer of cryo-thawed cleavage-stage embryos obtained from successful fresh treatment cycles compared with those obtained from cycles which failed. By contrast, a study of 243 frozen blastocyst transfer or FBT cycles by Berin et al. (2011) indicated that fresh cycle outcome had no influence on the outcome of a subsequent frozen cycle.

A growing body of evidence from studies on FET cycles indicates that endometrial receptivity is impaired following ovarian stimulation, a phenomenon which is not observed when undergoing a natural frozen embryo replacement cycle (Shapiro et al., 2011). A matched-cohort comparison of SET patients in fresh and FET cycles showed that overall the on-going CPR was significantly greater in the frozen–thawed group than the fresh group, for both Day 5 and Day 6 blastocysts (Shapiro et al., 2013). Further such evidence is provided by Roque et al. (2013) and Cohen and Alikani (2013). Overall, the data suggest that clinics should consider both the timing of cryopreservation and the possible negative effect of ovarian stimulation on endometrial receptivity associated with fresh cleavage-stage embryo or blastocyst transfer during a stimulated treatment cycle.

Provision of a safe, effective IVF programme is paramount. A recent meta-analysis by Maheshwari et al. (2012) reported that the risks of perinatal mortality, low birth weight, pre-term birth and antepartum haemorrhage are lower in pregnancies resulting from cryopreserved embryos when compared with pregnancies from fresh embryo transfers. Significantly improved neonatal outcomes were observed in a study comparing SET of vitrified-warmed blastocysts to fresh transfers (Roy et al., 2014). Although LBRs were similar, improvements were also seen for gestational age and birth weight. This is important, since ovarian stimulation in fresh cycles may be one contributor to underlying low birth weight in IVF babies (Schieve et al., 2002; Imudia et al., 2012), and correspondingly, FETs might show improved perinatal outcomes (Imudia et al., 2013). In particular, research should be directed at the routine use of cryopreservation in clinical IVF treatment, including assessments of efficacy, safety and cost-effectiveness. Although outcomes appear improved for FETs, greater understanding and research into modifiable risk factors during the process is also required to reduce disparity between the outcome of ART and non-ART infants (Hansen & Bower, 2014). Long-term follow-up studies of children would also be beneficial to evaluate the outcome of such strategies.

As evidence gathers in support of FET as a front-line treatment, significant developments have been observed in cryopreservation protocols. There is increasing usage of vitrification worldwide (Brison et al., 2012) particularly for blastocyst cryopreservation, with several studies reporting high survival rates and implantation rates for embryos and blastocysts (Edgar & Gook, 2012). Whilst evidence suggests that cleavage-stage embryos can be cryopreserved equally effectively using slow cooling and vitrification, blastocyst survival rates seem consistently higher with vitrification (Edgar & Gook, 2012). The ACE consensus meeting (Brison et al., 2012) and the ALPHA consensus meeting (ALPHA, 2012) highlighted the lack of well-designed prospective studies to determine whether one method should be preferred clinically to the other and stressed the need for further research to optimise process and methodology with respect to outcome and safety.

Whichever method is used for cryopreservation and thawing, it is recommended that centres should continually audit their performance and develop their MBR strategy to include FET cycles.

Recommendations – Cryopreservation strategies

1. An effective eSET strategy should include both fresh and subsequent frozen cycles, i.e. a ‘full cycle’ of treatment. (A)

2. Clinics should optimise cryopreservation methodology to ensure good survival rates and LBRs are maintained throughout a full cycle of treatment. (B)

3. Prospective RCTs are required to evaluate the efficacy of different cryopreservation strategies when adopted in an eSET programme. (B)

4. Long-term follow-up studies of children following treatment involving the use of frozen embryos and blastocysts are required. (B)

5. Further research is required to investigate the highly variable results obtained from frozen treatment cycles in different IVF centres. (C)

6. Further research is required into the efficacy of the ‘freeze all, replace later’ strategy. (C)

Patient education

A review of patients’ views on eSET was carried out by Leese and Denton (2010), and Roberts et al. (2010b) presented further research into UK patient perspectives. Many patients perceive patient selection (be it mandatory or voluntary) included in an SET programme as unfair and view the risk of twins from DET as acceptable within the boundaries of their own personal circumstances. The requirement for additional treatment cycles to achieve the same probability of success is regarded by some patients as physically and emotionally burdensome, and to some extent unnecessary. Inadequate patient education has often been held responsible for couples rejecting a clinical recommendation in favour of eSET, and even when fully informed of the available options surrounding eSET, many patients would still opt for DET. That said, it is encouraging that although some patients still expressed a desire for twins rather than singletons, the evidence suggested that eSET could become increasingly accepted especially if success rates approached or improved upon those of DET. Rai et al. (2011) concluded that the wish to have DET was driven by a desire to achieve a pregnancy and the perceived increase in success when replacing two embryos. Providing couples with more information about the potential risks of DET is an effective way to change their attitude towards eSET. It was reported that advice from the patient's clinician strongly influenced their decision regarding the number of embryos to replace. The paper also highlighted that women failed to recognise the social impact of a twin birth, suggesting that promoting the effectiveness of SET through emphasising tangible benefits such as improved long-term offspring health would be beneficial. Clearly patients need robust, detailed information to help them make an informed decision about eSET. Hope et al. (2008) showed that by exposing patients to information via an educational DVD on the outcomes and risk of twin pregnancies they were much more likely to accept eSET compared with those provided with standard reading material alone.

Recommendations – Patient education

1. The desire for patients to have more than one child needs to be taken into consideration and eSET policies and funding should allow for the transfer of all embryos of suitable quality regardless of earlier outcome if eSET is not to be perceived as disadvantageous. (B)

Multiple birth reduction strategies

UK clinics are required to have a MBR strategy and to monitor and audit this strategy. As evidence emerges on the issues of embryo selection and cryopreservation technologies, it is clearly necessary to audit and revise this strategy regularly. However as multiple births are a relatively rare event in any single clinic the absolute numbers of twins in a given audit period of 12 months or less will be too low to reveal anything but the most gross departures from a target value. Thus a more rounded, multifactorial approach to audit and review is required which examines the policy as implemented compared with the best practice in the sector. Such a review will include the selection of patients for DET, particularly the use of policy exceptions and discretionary areas, the use of cryopreservation, and patients’ views on acceptability.

Recommendations – Multiple birth reduction strategies

1. The individualisation of an eSET algorithm based solely on MBRs in an individual clinic is not recommended. Clinics should review their policies in the light of best practice determined across the sector. (GPP)

2. Centres should avoid basing decisions to change practice on small numbers of events within the normal range of statistical variation. (GPP)

3. Centres committed to eSET who are working towards achieving, or have attained and continue to maintain, a low MBR should take steps to evaluate the effectiveness of their eSET algorithm with respect to the timing of transfer, the selection of embryos for transfer and their cryopreservation strategy. (GPP)

4. Although there is evidence of a sustained reduction in the UK MBR it is imperative that centres audit their own policies and practice at least annually with the long-term aim of continually and sustainably reducing their MBR over time. Audit should focus on ensuring good practice rather than responding to small numbers of multiple births above or below a target rate. (GPP)

Cost implications and commissioning considerations

Multiple pregnancies are associated with a broad range of complications for both mother and child which in turn lead not only to higher antenatal and postnatal care costs but potential lifelong costs due to requirements for both medical and social support. The cost-effectiveness of implementing an eSET strategy has been comprehensively analysed in many different countries. Early work by Gerris et al. (2004) showed, in a non-randomised study, that the transfer of a top-quality embryo was associated with significantly lower costs in women under 38 years during their first cycle. This observation was confirmed by Kjellberg et al. (2006) with respect to the costs associated with complications of multiple pregnancy. Many studies support the cost-effectiveness of eSET especially when cumulative rates with frozen embryo replacement cycles are taken into consideration with Scotland et al., (2011) providing a UK perspective.

An attitude of responsibility must be adopted to ensure avoidable costs are limited through an eSET policy so burden is not placed on an already stretched NHS. This in turn may allow more effective allocation of already stretched and limited NHS funding resources to the commissioning of assisted conception treatment services.

Recommendations – Cost implications

1. Ensure commissioners are aware of the cost savings for both neonatal and long-term offspring care from adopting an eSET policy. (B)

2. Clinics should continue to support the campaign for NICE guidelines for funding provision and fair and equal provision of fertility treatment to all. (GPP)

The role of the HFEA

Achieving HFEA multiple birth targets

Since the HFEA established MBR limits in 2008, a significant shift in practice has been observed in favour of eSET, with the effect of reducing MBR in the vast majority of UK-licensed fertility centres. The key shifts in practice are summarised by the HFEA in their Multiple Births Year 4 Target Authority Paper (Darby, 2012):

• Since January 2008, the proportion of eSETs performed has increased across the sector. In 2008, 39,000 embryo transfers were performed, of which 1,919 (4.9 %) were eSET. In 2012, 50,219 embryo transfers were performed, of which 11,152 (22.2 %) were eSET.

• Since 2008 there has been a steady increase in the proportion of embryos transferred at the blastocyst stage. This has increased from 8.7 % of all embryo transfers in January 2008, to 48.7 %, in December 2012.

• MPR has decreased from 26.6 % in 2008 to 18.4 % in 2012. The decrease is most pronounced in women aged 18–34 years, who saw the greatest increase in eSET during this time.

• MBR closely follows the MPR, showing a continuing decline between 2009 and 2013, most notably in women aged 18–34 years, summarised in Figure 1.

• Pregnancy and LBRs have remained broadly steady since the introduction of the eSET initiative in 2008 through to 2013.

Figure 1. Comparison of Clinical Pregnancy Rate (CPR), Multiple Pregnancy Rate (MPR) and Multiple Birth Rate (MBR) in women of all ages, fresh and frozen transfers combined (most recent HFEA data, personal communication). Note: MPR data for 2014 and MBR data for 2013 are based upon mid-year figures (HFEA, 2015).

Compliance with MBR recommendations

Since the introduction of the MBR limit in 2008–2009 and an annual reduction in the target MBR thereafter, it is clear that clinics continue to find difficulty in meeting the target rate given that the national MBR rate remains at 15 % (HFEA, 2015).

Although the majority of clinics cannot be shown statistically to exceed the 15 % and 10 % target rates, the sector has still found compliance a challenge. The small numbers of twins seen in any one clinic mean that only a very few clinics are showing MBR rates which are statistically significantly above the target. The issue of how to deal with clinics that fail to meet the HFEA recommended MBR limit, some of which may well have adopted an eSET policy which is compliant with the best practice recommendations, remains a challenge for the sector. Conversely the low power to detect non-compliance based on individual clinic MBR implies that poor MBR reduction policies are unlikely to be detected by simple monitoring of outcomes. Only by working together can the sector and the HFEA ensure that best standards of patient safety and treatment efficacy are achieved in fertility centres across the UK and that the data currently published via the Choose a fertility Centre (CaFC) tool provide a fair and meaningful reflection of an individual clinic's performance irrespective of its size and treatment cycle throughput.

Reporting of treatment outcome results

The original ACE/BFS eSET guidance (Cutting et al., 2008) concluded that the HFEA reporting of results was not conducive to an eSET strategy and in the intervening period the situation has not much improved. That said, at the time of writing, the HFEA are undertaking a stakeholder review and consultation process on the future presentation of clinic results via CaFC, as part of the Information for Quality (IfQ) Programme. The intention is to highlight those clinics demonstrating an effective, safe eSET policy and to provide information to patients in a more meaningful, transparent way. A shift away from reporting LBR per cycle started towards LBR per embryo transferred and cumulative LBR from full cycles of treatment (including the transfer of fresh and subsequent frozen embryos) would improve the value of the data for patients trying to select a safe and effective treatment provider. There is also a need for more rounded provision of information on the outcomes of the component processes that make up an IVF treatment cycle. This is a clear priority area for research as this is the first time the UK will have changed the method of results presentation for more than 20 years.

Recommendations - HFEA

1. The HFEA should make changes to the way clinic data are reported. Clinic outcome data should be represented as LBR per embryo transferred and as cumulative LBR from fresh and FETs, which constitute a ‘full cycle’ of treatment. (C)

2. Future amendments to the way the HFEA present their ‘Choose a Fertility Clinic’ data to the public should highlight those clinics whose MBR is and remains low as being good examples of safe and effective practice. (C)

3. Further research is required into appropriate outcome measures which capture the complexity of the IVF process and their presentation. (C)

4. Multiple pregnancy is one of the most significant risks of fertility treatment and is to some extent avoidable. Fertility centres must continue to show a sustained commitment to reduce their MBR year-on-year to its lowest achievable value. (A)

Summary of Recommendations

Recommendations for fertility clinics

1. There should be a continued focus on minimising MBRs from IVF treatment by utilising an effective, dynamic eSET strategy. (GPP)

2. In situations where embryo quality is poor, clinics should consider the transfer of two embryos. An effective eSET policy should accommodate this. (B)

3. Centres should audit eSET rates, selection criteria and MBRs and where their dataset is robust, consider adjusting their eSET algorithm in line with their results on at least an annual basis, focussing on good practice rather than small numbers of multiple births above or below a target rate. (GPP)

4. Maximising oocyte and embryo quality is an essential part of an effective eSET strategy; a focus should remain on optimising superovulation regimens. (A)

5. Patients should be counselled that current best evidence indicates that blastocyst stage transfer may result in a successful outcome sooner, but with some specific increased risks, and may ultimately lead to a reduction in the overall chance of success. (A)

6. An effective eSET strategy should include both fresh and subsequent frozen cycles, i.e. a ‘full cycle’ of treatment. (A)

7. Clinics should optimise cryopreservation methodology to ensure good survival rates and LBRs are maintained throughout a full cycle of treatment. (B)

8. The desire for patients to have more than one child needs to be taken into consideration and eSET policies and funding should allow for the transfer of all embryos of suitable quality regardless of earlier outcome if eSET is not to be perceived as disadvantageous. (B)

9. The individualisation of an eSET algorithm based solely on MBRs in an individual clinic is not recommended. Clinics should review their policies in the light of best practice determined across the sector. (GPP)

10. Ensure commissioners are aware of the cost savings for both neonatal and long-term offspring care from adopting an eSET policy. (B)

11. Clinics should continue to support the campaign for NICE guidelines for funding provision and fair and equal provision of fertility treatment to all. (GPP)

12. The HFEA should make changes to the way clinic data are reported. Clinic outcome data should be represented as LBR per embryo transferred and as cumulative LBR from fresh and FETs, which constitute a ‘full cycle’ of treatment. (C)

13. Future amendments to the way the HFEA present their ‘Choose a Fertility Clinic’ data to the public should highlight those clinics whose MBR is and remains low as being good examples of safe and effective practice. (C)

14. Multiple pregnancy is one of the most significant risks of fertility treatment and is to some extent avoidable. Fertility centres must continue to show a sustained commitment to reduce their MBR year-on-year to its lowest achievable value. (A)

Recommendations for the management and review of clinic eSET algorithm

1. Where blastocyst transfer is performed, clinics should review their eSET data and criteria for extended embryo culture regularly. (GPP)

2. Centres with the resources to support time-lapse morphometric analysis may use this information to improve their eSET algorithm. (GPP)

3. Centres should avoid basing decisions to change practice on small numbers of events within the normal range of statistical variation. (GPP)

4. Centres committed to eSET who are working towards achieving, or have attained and continue to maintain, a low MBR should take steps to evaluate the effectiveness of their eSET algorithm with respect to the timing of transfer, the selection of embryos for transfer and their cryopreservation strategy. (GPP)

5. Although there is evidence of a sustained reduction in the UK MBR it is imperative that centres audit their own policies and practice at least annually with the long-term aim of continually and sustainably reducing their MBR over time. Audit should focus on ensuring good practice rather than responding to small numbers of multiple births above or below a target rate. (GPP)

Research recommendations

1. Further research is required (a) to validate the efficacy of eSET policies and (b) confirm the long-term safety of the culture and cryopreservation processes that constitute such policies. (C)

2. Prospective studies are required to determine the impact of embryo culture to the blastocyst stage on MZT, pre-term birth and associated epigenetic changes and on why MZT appears to be more prevalent in some clinics. (B)

3. Technological advances including time-lapse imaging and morphometric assessment show promise, as embryo selection and de-selection tools, but further high-quality prospective studies are required to develop and validate robust algorithms followed by RCTs to demonstrate their role in an eSET strategy. (C)

4. Further development and evaluation is required of the effectiveness of selecting embryos based on metabolic or related traits. (C)

5. Prospective RCTs are required to evaluate the efficacy of different cryopreservation strategies when adopted in an eSET programme. (B)

6. Long-term follow-up studies of children following treatment involving the use of frozen embryos and blastocysts are required. (B)

7. Further research is required to investigate the highly variable results obtained from frozen treatment cycles in different IVF centres. (C)

8. Further research is required into the efficacy of the ‘freeze all, replace later’ strategy. (C)

9. Further research is required into appropriate outcome measures, which capture the complexity of the IVF process and their presentation. (C)

Acknowledgements

The authors would like to thank the members of ACE and the BFS involved in reviewing this paper pre-submission, and Henry Leese and Allan Pacey for their review of this paper prior to final submission. We would also like to thank Suzanne Hodgson from the HFEA for providing us with the most up-to-date relevant national information available at the time of submission.

Declaration of interest: None