Arterial stiffness during controlled ovarian hyperstimulation and early pregnancy in women exposed to assisted reproduction

ABSTRACT

Introduction: Female sex hormones have vasorelaxing effects in non-pregnant and pregnant women. We aimed to investigate the effect of controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF), and early pregnancy, on arterial stiffness as assessed by digital pulse wave analysis (DPA), hypothesizing reduced arterial stiffness as an effect of increased estrogen levels.

Material and methods: A total of 68 women undergoing IVF were examined with DPA before conception and during IVF treatment with COH and embryo transfer (ET), and in gestational week seven in 19 women who became pregnant. Heart rate (HR), mean arterial pressure (MAP) and the DPA variables cardiac ejection elasticity index (EEI), b/a, dicrotic index (DI), d/a and aging index (AI) were measured.

Results: HR was significantly increased at all measuring points (p ≤ 0.003) but MAP only at ET (p 0.007). DPA variables representing large arteries (EEI, b/a) and peripheral arteries (DI, but not d/a), and the global variable AI, indicated increased arterial stiffness at ET compared with baseline (p ≤ 0.035). No DPA variable was significantly changed at pregnancy measurements compared to baseline.

Conclusion: During COH for IVF treatment, DPA showed no changes in arterial stiffness during the follicular phase or in early pregnancy, but increased arterial stiffness in central and peripheral arteries in the early luteal phase. The result suggests a hormonal hemodynamic activation counteracting the effects of estrogen.

KEYWORDS:

• arterial stiffness
• digital pulse wave analysis
• controlled ovarian hyperstimulation
• pregnancy
• in vitro fertlization

Introduction

There is both experimental and epidemiological evidence that female sex hormones have beneficial effects on the vascular system. Receptors for estrogen and progesterone are found in the vascular endothelium and smooth muscle cells (1), through which vascular tone can be regulated (2). Within 3 days of estrogen treatment, ovariectomized ewes show drops in mean arterial blood pressure (MAP) and total vascular resistance, and associated increases in heart rate (HR) and cardiac output (CO) (3). Aortic compliance is greater in women compared to men of the same age, and the age-dependent degenerative changes of the vessel wall are postponed in women (4). Estrogen, and possibly also progesterone, decreases vascular tone through nitric oxide mediated vasodilation (1) as well as through a structural modification of the vessel wall matrix (5), both of which can explain the gender differences with lower incidence of cardiovascular morbidity in women until menopause (1,2).

A person’s vascular condition can be expressed as arterial stiffness, which describes the buffer capacity of elastic arteries to ensure optimal blood flow and reduce pressure load on vessel walls and target organs. Arterial stiffness is determined by hemodynamic factors, including structural and functional properties, and is a strong independent risk factor of cardiovascular morbidity and mortality (6,7). Arterial stiffness is classically assessed by applanation tonometry and pulse wave analysis (PWA) of peripheral arteries, commonly expressed as pulse wave velocity (PWV) and augmentation index (AIx), which also provides information of endothelial function and arterial pressure wave reflections (8). Digital pulse wave analysis (DPA) is more simple to perform than applanation tonometry and has been suggested as a quick and operator-independent alternative method for estimation of arterial stiffness and endothelial function. DPA variables have shown good correlations to age and cardiovascular pathology and morbidity (9,10). We have previously reported robust repeatability of DPA variables, as well as correlations to the tonometry variables PWV and AIx (11).

Arterial vascular properties are affected by hormone replacement therapy (HRT) and endogenous hormonal fluctuations. HRT is associated with lower arterial stiffness (12), which is in congruence with current evidence of a beneficial effect of HRT on cardiovascular risk, at least during the first decade after menopause (13). In controlled ovarian hyperstimulation (COH) for in vitro fertilization (IVF), multiple follicles are developed by administration of injectable gonadotrophins (follicle-stimulating hormone [FSH] or human menopausal gonadotropin [hMG]), and follicle-derived estrogens then increase to supranormal levels (14). To our knowledge, there are no previous studies investigating the effect of COH on arterial stiffness.

Pregnancy is a state with increased female sex hormone levels and a hyperkinetic low resistance circulation. Already in the first weeks of pregnancy, total vascular resistance (TVR) is reduced and arterial compliance increased with reduced pulse wave reflection, possibly due to the vasorelaxing effects of estrogen (15–18). A slight increase in TVR is then seen towards term (15). In accordance with TVR changes, arterial stiffness parameters show a U-shaped relation to gestational age (19–22), but studies in very early gestation and studies using DPA in pregnancy are scarce.

In this longitudinal study we aimed to investigate the effect of COH and very early pregnancy on arterial stiffness assessed by DPA. We hypothesized that COH and early pregnancy would have vasodilatory effects and reduce arterial stiffness in central and peripheral arteries.

Methods

Patient selection and study protocol

Women seeking for infertility at the Nordic IVF Malmö clinic, Sweden, and whom were planned for IVF treatment, were asked to participate. The clinic is a private facility which treats women who are not entitled to publically financed IVF within the Swedish health care system. To be enrolled in the study, women had to speak and understand Swedish. Exclusion criteria were known cardiovascular disease or diabetes, or ongoing medical treatment with substances having cardiovascular effects. Women with inhalation treatment for asthma or levothyroxine were allowed in the study. The study was approved by the Regional Research Ethics Committee in Lund (Dnr 2014/648) and all women gave their oral and written informed consent. The women were not exposed to any deviation from the planned IVF treatment and no medical interventions or invasive procedures were performed because of the study.

Arterial stiffness measurements were performed at the first out-patient visit to the clinic (basal measurement), then at the first ultrasound scan during ovarian stimulation (day 7–8 of FSH or hMG treatment, stimulation measurement), and a third time after embryo transfer (ET) (ET measurement). In women who became pregnant, ultrasonography was booked in gestational week seven and DPA measurements were performed then.

Controlled ovarian hyperstimulation

In preparation for IVF treatment, two different protocols were used, a long gonadotropin-releasing hormone (GnRh) agonist or a short GnRH antagonist protocol. Women who received the long protocol were treated with the GnRH agonist nafarelin nasal spray 200 μg/dose (Synarela®, Pfizer AB, Sollentuna, Sweden). Nafarelin nasal spray was started on cycle day 21 in the menstrual cycle preceding ovarian IVF stimulation and given in a dose of 400 μg twice daily. In women following the short protocol, the GnRh antagonist ganirelix 0.25 mg (Orgalutran®, Merck Sharp & Dohme AB, Stockholm, Sweden) was injected subcutaneously daily from stimulation day 5 until the day of human chorionic gonadotropin (hCG) administration.

For ovarian stimulation, gonadotrophins were given, either as follitropin alfa (GONAL-f®, Merck Sharp & Dohme AB, Stockholm, Sweden; Bemfola®, Gedeon Richter Plc, Budapest, Hungary), follitropin beta (Puregon®, Merck Sharp & Dohme AB, Stockholm, Sweden), menotropin (Menopur®, Ferring Läkemedel AB, Malmö, Sweden), or urofollitropin (Fostimon®, HB Medical ApS, Hörsholm, Denmark). The follicular growth was followed by serial transvaginal ultrasound scans and oocyte maturation was induced with recombinant hCG (Ovitrelle®, 250 μg, Merck Sharp & Dohme AB, Stockholm, Sweden) when the mean diameters of leading follicles were 18–20 mm. Oocyte retrieval was then scheduled 36 h after the hCG injection. Oocyte retrieval was performed transvaginally under ultrasound guidance in conscious sedation with fentanyl 1 μg/kg IV (Fentanyl®,50 μg/mL, B. Braun Medical AB, Danderyd, Sweden). Propofol 20–40 mg IV (Propofol-®Lipuro, B. Braun Medical AB, Danderyd, Sweden) was given when needed. Embryos were cultured in SAGE 1-Step^TM medium (ORIGIO a/s, Måløv, Denmark). Embryo transfer was performed with a Cook Sydney IVF embryo transfer catheter set (Cook Medical, Bloomington, Indiana, USA).

ET was performed on day 2, 3 or 5 after egg retrieval, depending on embryo development. Progesterone vaginal tablets 100 mg (Lutinus®, Ferring Läkemedel AB, Malmö, Sweden) were given for luteal support three times daily until time of pregnancy test. The pregnancy test was performed 20 days after the day of oocyte retrieval.

The ovarian responsiveness to gonadotropin stimulation was estimated with ovarian sensitivity index (OSI), as defined by Huber et al. (23). OSI describes the ratio between oocyte yield and total dose of FSH: number of retrieved oocytes ×1000 divided by the cumulative FSH dose administered. The authors define a poor ovarian response as OSI < 1.697/IU, normal response as OSI 1.697–10.07/IU, and a high response as OSI >10.07/IU, corresponding to mean ± 1SD on the logarithmic curve after antilogarithmation. Thus, when OSI is used as a continuous variable the logarithmic value should be calculated (logOSI).

Digital pulse wave analysis

After resting for 10 min in the supine position in a single room with minimum disturbances, the blood pressure (BP) was measured using an automatic BP monitor (Omron M3, Omron Healthcare Europe, Hoofddorp, The Netherlands). MAP was defined as diastolic BP + (systolic BP − diastolic BP)/3.

When still in the supine position, two consecutive DPA recordings of 70 s each were performed using a Meridian™ DPA photoplethysmograph (Salcor AB, Uppsala, Sweden) connected to a laptop (HP 625, Hewlett Packard, Solna, Sweden). The mean value of the two recordings was used for further calculations. With a pulse oximetry finger clip placed distal on the left index finger, a photoelectric plethysmography (PPG) volume pulse wave curve is created. The compound waveform represents the forward-going pulse wave from the heart (percussion wave) and the reflected wave from peripheral arteries (tidal wave). The pulse wave contour is influenced by the elasticity of the arterial walls and can be mathematically analyzed. The Meridian™ DPA apparatus automatically generates HR and 16 different pulse wave indices of arterial function based on the PPG waveform contour and its second derivative (acceleration PPG, called APG), and can to some extent separate arterial stiffness in central and peripheral vessels (10). The physiological background of PPG contour analysis has previously been described by Millasseau et al. (24), and we have described the physiological and mathematical background of DPA variables and validated the Meridian™ DPA indices (11). Based on our previous findings of repeatability and correlation to applanation tonometry variables (11), we chose to restrict the analysis to five DPA indices: cardiac ejection elasticity index (EEI) and b/a for stiffness in central arteries and left ventricular capacity, dicrotic index (DI) and d/a for peripheral arteries, and aging index (AI) for systemic arterial stiffness. A physiological interpretation of the DPA variables is presented in Table 1.

Table 1. Description of digital pulse wave analysis (DPA) variables and effects of physiological conditions.

DPA variables	Physiological interpretation	Conditions with high values	Conditions with low values
Cardiac ejection elasticity index (EEI)	Indicates left ventricular ejection capacity or compliance of central arteries	Large artery compliance, increased left ventricle ejection power	Large artery stiffness, atherosclerosis, decreased left ventricular ejection power
Dicrotic index (DI)	Indicates level of resistance in the peripheral circulation	Peripheral vasoconstriction	Peripheral vasodilatation
b/a	Indicates left ventricular ejection power or central artery compliance	Low central artery compliance, increased cardiovascular risk, atherosclerosis, increases by age	High compliance of central arteries; young age, athletic constitution
d/a	Reflects the intensity of the reflecting pulsewave from peripheral arteries, indicative of afterload	Young age, peripheral vasodilatation	A longer negative d peak develops by advancing age, atheriosclerosis, peripheral vasoconstriction
Aging index (AI)	AI = (b-c-d-e)/a, representing the global vascular stiffness, i.e. “vascular age”	Atheriosclerosis, increases by age	Young age, athletic constitution

Since the DPA method cannot separate decreased arterial compliance caused by structural changes of the vessel wall from vasoconstriction or intravascular volume expansion, the term arterial stiffness is used interchangeably in this paper.

Statistical methods

Associations between continuous variables were tested with Kendall tau rank correlation, and paired longitudinal continuous variables compared with Wilcoxon matched-pairs signed-rank test. Comparisons between multiple groups of unpaired continuous variables were performed with the Kruskal–Wallis test, and in two-group comparisons with the Mann-Whitney U test. When significant associations between multiple continuous variables were found, first simple and then multiple linear regression analysis were performed to investigate variable independency. A two-sided p value <0.05 adjusted for ties was considered significant. The StatView version 5.0.1 (SAS Institute, Cary, NC), MedCalc (MedCalc Software, Mariakerke, Belgium) and IBM SPSS version 23.0 (IBM Corp., Armonk, NY) computer software programs were used for statistical calculations.

We have previously shown that some of the DPA variables used in the present study are HR dependent (11). Hence, if a DPA variable showed a statistically significant association with HR at the basal measurement, and if the HR at the intervention measurement (i.e., at ovarian stimulation on day 7–8, at ET, or in pregnancy) had changed significantly, a simple linear regression analysis was performed; if then significant, the DPA variable in question was adjusted to a HR of 75 bpm (DPA@75) with the equation DPA@75 = DPA + C(75-HR). C denotes the slope constant.

Results

A total of 93 women were enrolled in the study. After excluding drop-outs due to not completing the FSH stimulation protocol, insufficient data collection, or data loss (the laptop computer was stolen), 68 women remained for analysis at baseline, 59 women at stimulation measurement, and 52 women who completed ET. Table 2 shows the demographic characteristics.

Table 2. Demographic data of the study population.

	n = 68
	Median (range)	Mean (SD)
Age (years)	36 (26–44)	36 (5)
BMI (kg/m^2)	24 (18–35)	24 (4)
MAP (mmHg)	86 (68–134)	87 (10)
HR (bpm)	68 (42–87)	67 (10)
Parity (n)	1 (0–4)	–
FSH (IU)	1875 (822–5850)	2114 (989)
Follicles (n)	12 (2–28)	13 (6)
Oocytes (n)	10 (2–23)	10 (6)
OSI (n × 1000/IU)	4.8 (0.67–21.9)	5.9 (4.4)
Infertility factor	(n)
Male	22
Anovulation	6
Tubal	4
Endometriosis	4
Unidentified	32
IVF protocol	(n)
Agonist	11
Antagonist	57

SD, standard deviation; BMI, body mass index; MAP, mean arterial pressure; HR, heart rate; FSH, follicle stimulating hormone; OSI, ovarian sensitivity index (number of retrieved oocytes x 1000 divided by the cumulative FSH dose); IVF, in vitro fertilization.

DPA measurements during FSH stimulation were performed on average at day 7 (mean 7, median 7, interquartile range 7–8). A total of 25 women became pregnant, of whom DPA measurements were performed in 19. Pregnancy measurements were performed at 7 + 0 to 7 + 6 weeks of gestation, except in two women where measurements were made at 6, in one woman at 9 and one woman at 10 weeks, respectively.

Using the cut-off values of OSI, 9 women were classed as poor, 49 as normal, and 10 as high ovarian responders.

Baseline measurements

Associations between baseline DPA measurements and maternal age, HR and OSI are shown in Table 3. Since EEI and DI were significantly related to HR, and HR significantly increased at interventions (Table 4), EEI was adjusted to EEI@75 and DI to DI@75 at these statistical calculations.

Table 3. Associations at baseline measurements between DPA variables and maternal age, heart rate, logarithmic value of ovarian sensitivity index (logOSI) and grade of ovarian response at controlled ovarian hyperstimulation.

	Maternal age		Heart rate		LogOSI		Ovarian response
DPA variables	p^a	Tau^a	p^a	Tau^a	p^a	Tau^a	Poor Median (95% CI)	Normal Median (95% CI)	High Median (95% CI)	Poor vs. normal vs. high^c	Poor vs. normal^d	Normal vs. high^d	Poor vs. high^d
EEI	<0.0001^b	−0.40	0.045^b	0.17	0.0002^b	0.31	0.45 (0.30, 0.57)	0.60 (0.49, 0.69)	0.66 (0.56, 1.08)	0.013	0.044	0.12	0.001
b/a	0.0001^b	0.32	0.70	–	<0.0001^b	−0.34	−0.53 (−0.58, −0.39)	−0.60 (−0.65, −0.54)	−0.63 (−0.75, −0.60)	0.010	0.046	0.12	0.0002
DI	0.016^b	0.20	<0.0001^b	−0.51	0.34	–	0.80 (0.71, 0.90)	0.74 (0.68, 0.79)	0.74 (0.57, 0.85)	0.23	N/A	N/A	N/A
d/a	0.0003^b	−0.30	0.79	–	0.029^b	0.18	−0.18 (−0.31, −0.14)	−0.17 (−0.20, −0.14)	−0.13 (−0.20, −0.06)	0.12	N/A	N/A	N/A
AI	0.0002^b	0.31	0.68	–	0.0004^b	−0.29	−0.36 (−0.45, −0.04)	−0.54 (−0.61, −0.32)	−0.53 (−0.82, −0.43)	0.039	0.092	0.24	0.001

DPA, digital pulse wave analysis; EEI, cardiac ejection elasticity index; DI, dicrotic index; AI, aging index; OSI, ovarian sensitivity index; N/A, not applicable.

^a Statistics with Kendal tau rank correlation analysis.

^b p < 0.05 confirmed with simple linear regression analysis.

^c Statistics with Kruskal-Wallis test.

^d Statistics with Mann-Whitney U test.

Table 4. Hemodynamic effects of oocyte stimulation and pregnancy, compared with basal measurements before conception. For details, see text. Digital pulse wave analysis values are indices without quantitative measures.

	Basal n = 68	Stimulation n = 59			Embryo transfer n = 52			Pregnancy n = 19
	Median (95% CI)	Median (95% CI)	p	Effect^a	Median (95% CI)	p	Effect^a	Median (95% CI)	p	Effect^a
MAP (mmHg)	86 (84, 90)	84 (83, 86)	0.57	–	89 (85, 93)	0.007	Increase	85 (80, 90)	0.91	–
HR (bpm)	68 (65, 71)	72 (68, 75)	0.0003	Increase	75 (72, 79)	<0.0001	Increase	77 (73, 85)	0.003	Increase
EEI@75	0.630 (0.562, 0.691)	0.630 (0.535, 0.692)	0.66	–	0.533 (0.459, 0.688)	0.021	Increased large artery stiffness, decreased LV power	0.501 (0.477, 0.590)	0.75	–
b/a	−0.600 (−0.630, −0.550)	−0.585 (−0.650, −0.535)	0.86	–	−0.563 (−0.625, −0.490)	0.035	Increased large artery stiffness, decreased LV power	−0.530 (−0.600, −0.505)	0.15	–
DI@75	0.691 (0.652, 0.715)	0.692 (0.642, 0.702)	0.77	–	0.710 (0.676, 0.737)	0.003	Peripheral vasoconstriction	0.705 (0.592, 0.773)	0.16	–
d/a	−0.170 (−0.190, −0.145)	−0.165 (−0.190, −0.145)	0.65	–	−0.198 (−0.235, −0.140)	0.15	–	−0.195 (−0.265, −0.110)	0.30	–
AI	−0.455 (−0.565, −0.360)	−0.460 (−0.545, −0.375)	0.37	–	−0.355 (−0.480, −0.205)	0.008	Increased global arterial stiffness	−0.350 (−0.470, −0.230)	0.14	–

HR, heart rate; MAP, mean arterial pressure; EEI@75 ejection elasticity index corrected to heart rate 75 bpm; DI@75, dicrotic index corrected to heart rate 75 bpm; AI, aging index; LV, left cardiac ventricle.

^a Effect compared to basal measurement, statistics performed with Wilcoxon matched-pairs signed-rank test.

EEI and b/a indicated that older age was associated with stiffer large arteries, and DI and d/a indicated stiffer small arteries; the AI indicated a global arterial stiffness (Table 3). LogOSI was negatively associated with age (p < 0.0001, tau −0.35), indicating a lower ovarian sensitivity at higher age.

EEI, b/a, d/a and AI, but not DI, indicated a positive association between arterial elasticity and ovarian response. EEI, b/a and AI indicated higher arterial stiffness in poor responders. When including maternal age and logOSI in multiple regression analyses, significant associations with logOSI remained for AI (p = 0.032) and b/a (p = 0.008), but not for EEI (p = 0.14) and d/a (p = 0.61); maternal age remained being an independent determinant of arterial stiffness (p ≤ 0.0015).

There were at baseline measurements no significant differences in DPA variables between women receiving COH according to antagonist (n = 57) or agonist (n = 11) protocols (p ≥ 0.21).

The group who ultimately became pregnant did not differ significantly from the non-pregnant group in BMI (p 0.092), age, MAP, logOSI or baseline DPA measurements (p ≥ 0.25).

Measurements at interventions

Table 4 and Figure 1 show the cardiovascular changes at measurement points. With exception for HR, which in comparison with the basal measurement increased at all interventions, variables changed significantly only at ET: an increase in MAP was paralleled by increases in arterial stiffness variables representing both peripheral (DI, but not d/a) and central arteries (EEI, b/a) compared to baseline. AI, representing global arterial stiffness, was also significantly changed toward stiffness at ET.

Figure 1. Boxplots showing cardiovascular changes after administration of follicle-stimulation hormone (Stim), at embryo transfer (ET) and in early pregnancy (Gravid) compared to baseline values (Basal). Gray boxes indicate significant changes (p < 0.05) compared with basal measurements, and star symbols denote values outside the panel boxes. HR, heart rate; MAP, mean arterial pressure; AI, aging index; EEI@75, cardiac ejection elasticity index adjusted to heart rate 75 bpm; DI@75, dicrotic index adjusted to heart rate 75 bpm.

Calculated from baseline to ET (i.e. DPA value at ET minus DPA value at baseline), there were no significant differences in delta DPA values (for d/a p = 0.066, other p ≥ 0.27) between women in the agonist and antagonist protocols. Excluding the 11 women with agonist protocols from the analysis did not change the results at interventions.

There was no significant correlation (for b/a p = 0.07 and tau 0.17, other p ≥ 0.11) between the magnitude of change in DPA variables from baseline to ET (i.e. DPA value at ET minus DPA value at baseline) and logOSI. Including age in multiple regression analyses did not change significance levels, but b/a remained close to significant (logOSI p = 0.066; age p = 0.002).

In the group of women who became pregnant, no DPA variable changed significantly compared with the baseline value, but there was a significant increase in HR.

Discussion

Contrary to our hypotheses, we found an increased global arterial stiffness at ET in early luteal phase after COH for IVF, and no significant changes of DPA variables in early pregnancy. The effect of COH appears modest for all DPA variables, however. Since female sex hormones have vasodilatory effects (25), we expected COH to reduce arterial stiffness at stimulation as well as at ET and early pregnancy.

The hormone levels are expected to be well above normal after a week of FSH stimulation, but the stimulation measurements showed no significant DPA variable changes. It might have been too early in the stimulation course to see any vascular effect. Furthermore, female reproductive hormones have diverse effects through known and unknown mechanisms on multiple organ systems (26). The COH-induced hormonal situation is complex, and as for other steroid hormones, the effects of estrogen and progesterone may depend on individual responses and relative concentrations and bioactivity (27). Manau et al. found significantly reduced TVR after hCG-induced ovulation in IVF cycles (28). However, that study was small and had a proportionally high complication frequency (13%) of ovarian hyperstimulation syndrome, which might be hemodynamically different than uncomplicated COH. No previous studies on arterial stiffness during COH and IVF could enlighten us.

Previous studies of arterial elasticity in the normal menstrual cycle are inconclusive due to small study groups and different methodologies, showing either no changes (29,30) or increased arterial elasticity in the follicular phase, and decreased elasticity in the luteal phase (31–33). The only PPG study performed in the normal menstrual cycle confirmed the latter finding (34), while the few studies using applanation tonometry for assessment of vascular elasticity have shown no changes or increased elasticity in the luteal phase (18,35). Researchers have speculated that an absent vasodilatory effect or increased stiffness in the luteal phase are due to increased levels of progesterone, which is a potential vasoconstrictor (25), or activation of the renin-angiotensin-aldosterone-system (RAAS) or other hormones that counteract the estrogen effect (30,32). These explanations would support the results of increased arterial stiffness at ET in the present study.

The potential influence of RAAS deserves further consideration. Pro-renin exists in high concentrations in ovarian follicles and at hyperstimulation the plasma concentration after hCG is directly related to the number of ovarian follicles (36). In women undergoing COH for IVF, the RAAS is markedly activated with high levels of pro-renin, renin and angiotensinogen in plasma and high urine aldosterone concentration, peaking in the early luteal phase after ovulation induction with hCG (37,38). Angiotensin II increases central and systemic arterial stiffness (39), and we speculate that the increase in arterial stiffness found in our study could be an effect of angiotensin II, eclipsing a possible vasodilatory effect of estrogen. However, d/a, which previously has been shown to reflect the effect of angiotensin (10), was not significantly changed.

Another reason for the increased arterial stiffness at ET could be a volume expansion causing a decrease in vascular compliance. Estrogen and progesterone increase the plasma volume (40) and the DPA technique cannot separate increased stiffness based on structural changes in the arterial wall, vasoconstriction or increased volume load.

The majority of women responded normally to COH, as estimated by the OSI. Multiple factors influence the individual ovarian response to COH, but overall, estrogen levels increase tenfold in IVF compared to concentrations during the normal menstrual cycle, and continue to increase if pregnancy is achieved (14). OSI was not significantly associated with the increase in arterial stiffness for any DPA variable. However, OSI was developed to be a standardized definition of ovarian response and associate to clinical outcome, but not to reflect hormone levels. It might then be a too blunt surrogate variable to use for estimation of endogenous hormone response.

The study confirmed that stiffer arteries relate to older age (10), and also showed that with less elastic arteries the ovarian response was inferior. Age and OSI were both independently associated with arterial stiffness. These findings bring to mind trials to treat with low-dose aspirin to induce vasodilation and increased intraovarian circulation for improved folliculogenesis. A Cochrane meta-analysis from 2016 concludes that there is no evidence in favor of routine use of aspirin to improve pregnancy rates for a general IVF population (41), and the women who became pregnant in the present study did not show significantly different DPA values at baseline. However, if our observations can be reproduced in other studies, it would be worthwhile to explore the selective use of low-dose aspirin in women with stiffer arteries. The myocardium and conduction system of the heart contain sex steroid hormone receptors, and stimulation causes increased HR and ventricular hypertrophy (26). Consequently, HR increases in the first trimester of pregnancy (15). This is in congruence with our results of increased HR during the IVF protocol.

Previous studies of normal hemodynamic adaptation to pregnancy have shown decreased TVR and increased arterial compliance, detectable already at five weeks of gestation (17,42). Previous research with PWA starting in the late first trimester, have shown a decrease in arterial stiffness, expressed as AIx or PPG indices, reaching a nadir in the second trimester, and then increasing toward the end of pregnancy (18–22). In a study with preconceptional comparisons in spontaneous conceptions, reduced AIx was found already at six gestational weeks (43). However, we did not find any significant change of arterial stiffness at 7 weeks of gestation in those women who became pregnant. Although the series of 19 pregnant women is large enough for statistical comparisons with non-parametric statistics (44), there is a possibility of type II error. Furthermore, the study population was a selected group and not necessarily representative of average women. It could also have been too early in pregnancy to detect changes in arterial stiffness with the modality of DPA.

A strength of the study is that we have performed longitudinal measurements from before conception, during the reproductive cycle, and in into early pregnancy. The women were then their own controls. The results should be reviewed in the context of COH, but would have been practically hard to achieve other than in an IVF setting.

A weakness of the study is that no plasma hormone levels were determined, since that is not routine in our standard IVF treatment. The study protocol followed the clinical visits during the IVF treatment, but measurements at oovum pick up were refrained because of perioperative sedative treatment and expected confounding stress.

In summary, we found no changes in arterial stiffness as detected by DPA during the follicular phase or in early pregnancy, but increased systemic arterial stiffness in early luteal phase during COH for IVF treatment. This could be the result of a hemodynamic activation counteracting the effects of estrogen, possibly via the RAAS. In pregnant women monitored at seven weeks, we found no difference in arterial stiffness compared with preconceptional measurements. As previously found in other studies, compared with preconceptional measurements HR showed an increase at all measurement points.

Acknowledgments

Staff at Nordic IVF Malmö are gratefully acknowledged for practical contribution.

Disclosure statement

The authors report no conflict of interest.

Additional information

Funding

This study was supported by grants from Region Skåne and the Medical Faculty (ALF), Lund University, Sweden.