Stress-reducing interventions in pregnancy for the prevention of preterm birth: a systematic review and meta-analysis

Abstract

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality. Maternal stress during pregnancy is an established risk factor for PTB. We aimed to review the effects of stress-reducing interventions during pregnancy on PTB. Studies reporting on stress-reducing interventions during pregnancy and PTB rates in general low-risk obstetric populations were included. PTB rates, low birth weight (LBW) rates, mean gestational age and birth weight, maternal anxiety and stress, and adverse perinatal outcomes were investigated. Data were extracted using a standardized extraction form, pooled effect sizes were calculated with the random effects model. Ten studies with a total of 4.816 women were included. The interventions included Pilates, yoga, a multidisciplinary stress reduction program, combination therapy (combining mindfulness, yoga, music, baby bonding, and education), and hypnosis. The incidence of PTB was significantly lower in the intervention group (RR 0.50, 95% CI 0.35 − 0.71). The overall quality of the included studies was low, and the risk of bias was high. In conclusion, this study provides evidence supporting the potential efficacy of stress-reducing interventions in reducing the incidence of PTB in low-risk women. We propose a RCT of high quality to determine the effectiveness of stress-reducing interventions in reducing PTB risk.

Keywords:

• Hypnosis
• meditation
• mindfulness
• Pilates
• preterm
• stress-reduction
• yoga

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Correction

Introduction

Preterm birth (PTB), defined as birth before completing 37 weeks of gestation, remains a significant public health concern worldwide [1–3]. It is associated with numerous adverse outcomes, including neonatal mortality, long-term neurodevelopmental impairments, and substantial economic burdens on healthcare systems [4–6]. The etiology of PTB is multifactorial, involving a complex interplay of genetic, environmental, and behavioral factors [7,8]. Among these factors, maternal stress has gained considerable attention as a potential contributor to the occurrence of PTB.

Maternal stress, broadly encompassing various psychosocial, environmental, and physiological factors, has been implicated in disrupting the delicate balance of maternal-fetal interactions during pregnancy [9]. One important aspect of the stress response during pregnancy involves the activation of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis plays a crucial role in regulating the body’s response to stress. When activated, the HPA axis leads to the release of stress hormones, including corticotrophin-releasing hormone, adrenocorticotropic hormone, and cortisol [10]. This dysregulation can result in immune system dysfunction, vascular impairment, placental inflammation, impaired uteroplacental blood flow, and altered fetal programming, all of which contribute to an increased risk of PTB [11–14].

Previous research by Hedegaard et al. has highlighted the association between maternal stress and PTB. They reported that women experiencing one or more highly stressful life events during pregnancy had a 1.76-fold increased risk of PTB compared to women who did not encounter such events [15]. The same authors found that high psychologic distress levels in the 30^th week of pregnancy was associated with PTB, with a relative risk (RR) of 1.75 (95% CI 1.20 − 2.54) [16]. These findings have sparked the hypothesis that stress-reducing interventions may offer a promising approach to prevent PTB. Consequently, there has been a growing interest in exploring the effectiveness of stress-reducing interventions in the prevention of PTB. These interventions encompass diverse modalities such as mindfulness-based stress reduction, relaxation techniques, yoga, and hypnosis. While individual studies have explored the impact of these interventions on PTB, the results have been conflicting, and a comprehensive review of the available evidence is lacking. Therefore, the primary aim of this study was to assess whether stress-reducing interventions can reduce the incidence of PTB, specifically in a low-risk obstetric population. By conducting this analysis, we aimed to provide a comprehensive overview of the existing literature and elucidate the potential benefits of stress-reducing interventions in preventing PTB in this specific population.

Material and methods

Search strategy and selection criteria

This systematic review and meta-analysis was conducted in accordance with the PRISMA guidelines and registered in PROSPERO. A search was performed in MEDLINE, Embase, ClinicalTrials.gov, Cumulative Index to Nursing and Allied Health Literature, and the Cochrane Library, using the following search terms: (pregnancy OR "pregnant women") AND ("preterm labor" OR "preterm delivery" OR "birth weight" OR "birth outcome") AND ("mind-body" OR meditation OR yoga OR mindfulness OR "relaxation therapy" OR massage OR Taichi OR "guided imagery") (Appendix S1). The search encompassed English-written studies published from 1995 to April 2020. The original search was updated in January 2023. Studies focused on stress-reducing interventions and had to report PTB rates. Studies investigating women already in preterm labor (PTL), or specifically aiming at women at high risk of PTB or depression, or with a history of depression or anxiety disorders, were excluded. This review included randomized controlled trials (RCTs), controlled trials, cohort studies, and observational studies. Various interventions were investigated, including yoga, hypnosis, massage, deep breathing, relaxation techniques, and multidisciplinary stress reduction programs. This review did not include studies on group prenatal care, educational interventions, or social support interventions since these target factors other than stress reduction. The screening and selection of studies, as well as the assessment of bias using the Cochrane Risk of Bias Tool, were independently performed by two authors (LJ and AG). Disagreements were resolved through consultation with a third author (MB) until a consensus was reached.

Outcome measures

The primary outcome was the incidence of overall PTB, defined as both iatrogenic and spontaneous birth before completing 37 weeks of gestation [1]. Secondary outcomes were the incidence of LBW, defined as birth weight < 2500 grams, mean gestational age at time of birth, mean birth weight, maternal anxiety, maternal stress, and adverse perinatal outcomes [17].

Data analysis

Dichotomous outcomes were shown as RR along with their 95% confidence intervals (CI), while continuous data were shown as mean differences with their 95% CI. To calculate the pooled effect sizes, we collected the reported incidence rates, mean scores, standard deviations (SD), and participant numbers for each group separately. Missing SD were calculated using standard errors, confidence intervals, t-values, and p-values that related to the mean differences between the two groups. Where calculation was not feasible, the highest SD from studies in this meta-analysis were used. When analyzing three different groups, we performed grouping comparisons by comparing the intervention group with both the first and second control group, as well as comparing the first and second intervention groups with the control group. The Review Manager software (version 5.3.5) was used to calculate the pooled effect sizes, mean differences, create forest plots, and assess heterogeneity. Heterogeneity among the effect sizes was evaluated using the I² statistics, where values ranging from 0% (no heterogeneity) to 75% (high heterogeneity) were considered. To examine publication bias, we employed funnel plots for visual inspection. All pooled effect sizes were calculated with the random effects model.

Results

The initial search yielded a total of 1.602 studies. After removing duplicates, 1.196 titles and abstracts were screened, and a total of 1.166 studies were excluded. In addition, we identified two studies in the references of other systematic reviews. The reasons for exclusion are provided in Supplemental Table 1. Ultimately, ten studies met the eligibility criteria, as illustrated in Figure 1. Within the selection of ten included studies, there were five RCTs, one non-randomized trial, one longitudinal study, one prospective observational study, one clinical trial, and one study compared data with a historical control group. Table 1 provides a summary of the main characteristics of the included studies. In total, the reviewed studies encompassed 4.816 low-risk pregnant women and examined five different stress-reducing interventions. The interventions included Pilates, yoga, a multidisciplinary stress reduction program, combination therapy (combining mindfulness, yoga, music, baby bonding, and education), and hypnosis. All ten studies reported PTB rates [18–27], while four studies provided information on the incidence of LBW [20–23]. A total of six studies reported mean gestational age [18,19, 22–24, 27]. Additionally, seven studies provided results on mean birth weight [18,19, 22–24, 26,27]. Maternal anxiety was assessed in two studies using the State-Trait Anxiety Inventory (STAI) Scale [18,21]. The STAI Scale, developed and standardized by Spielberg et al. is a tool specifically designed to measure and distinguish between two types of anxiety: trait anxiety and state anxiety [28]. It comprises two separate scales, the STAI-1 and STAI-2, both consisting of 20 items with a maximum of four points per item. STAI-1 assesses the current, temporary state of anxiety related to a specific situation, while STAI-2 evaluates the general disposition of an individual to experience anxiety across different circumstances. Maternal stress was assessed in two studies using the Perceived Stress Scale (PSS) and Perceived Stress Reactivity Scale (PSRS) [19,22]. The PSS is a validated tool, designed to evaluate a person’s subjective perception of stress in their life by assessing the degree to which situations are appraised as stressful [29]. It measures the overall perception of stress experienced over a specific period. On the other hand, the PSRS is a validated tool which focuses specifically on an individual’s reactions to stressors. It aims to capture the emotional, cognitive, and physiological responses to stress. The PSRS assesses the extent to which stressors trigger various stress-related reactions [30]. Data were extracted by one author (AG) using a standardized data extraction form and fully checked by a second author (LJ).

Figure 1. Flowchart of the included studies.

Table 1. Included studies on stress-reducing interventions during pregnancy.

Author, year	Study type	Country	Selection criteria	Type of intervention	Number of participants	Outcomes	Conclusion
Aktan, 2021 [18]	RCT	Turkey	Pregnant women ≤35 years old, without pregnancy complications	IG: Childbirth training with pilates CG 1: Childbirth training alone CG 2: Usual care	IG: 21 CG 1: 21 CG 2: 22 Total: 64	PTB, gestational age, birth weight, maternal anxiety (STAI)	IG less anxious, no sign differences in PTB, gestational age and birth weight
Bhartia, 2019 [19]	RCT	India	Low risk pregnant women between 18-20 weeks’ gestation	IG: Yoga trice a week for 12 weeks CG: Usual care	IG: 38 CG: 40 Total: 78	PTB, gestational age, birth weight, maternal stress (PSS)	IG less stress, no sign differences in PTB, gestational age and birth weight
Bolanthakodi, 2018 [20]	RCT (single blinded, parallel randomized)	India	Primigravid women, 20–35 years, after 30 weeks’ gestation, without pregnancy and medical complications	IG: Yoga 7 sessions and trice a week CG: Usual care	IG: 75 CG: 75 Total: 150	PTB, LBW	IG less LBW, no sign differences in PTB
Consonni, 2010 [21]	Non randomized controlled trial	Brazil	Pregnant primigravid low risk women between 18-20 weeks’ gestation	IG: Multidisciplinary Program (education, kinesiotherapy, and relaxation techniques CG: Usual care	IG: 38 CG: 29 Total: 67	PTB, LBW, maternal anxiety (STAI)	IG less anxious, no sign differences in PTB and LBW
Malhotra, 2021 [22]	Longitudinal (panel) study	India	All pregnant women	IG: Baby care program (mindfulness, yoga, music, baby bonding and education) CG: Usual care	IG: 255 CG: 257 Total: 512	PTB, gestational age, birth weight, LBW, maternal stress (PSRS)	IG less stress, higher gestational age and birth weight, less PTB and LBW
Narendran, 2005 [23]	Prospective observational study	India	Healthy pregnant women, 18-35 years old, between 18-20 weeks’ gestation	IG: Yoga daily CG: Usual care	IG: 169 CG: 166 Total: 335	PTB, gestational age, birth weight, LBW	IG less PTB and LBW. No sign differences in mean gestational age and birth weight
Pais, 2021 [24]	RCT	India	Healthy pregnant women, 20-35 years old, between 18-20 weeks’ gestation	IG: Yoga daily CG: Usual care	IG: 61 CG: 63 Total: 124	PTB, gestational age, birth weight	IG less PTB, higher gestational age and birth weight
Reinhard, 2009 [25]	Comparison with historical control group	Germany	All pregnant women, between 28-34 weeks’ gestation	IG: Hypnosis CG: Usual care	IG: 64 CG: 2.135 Total: 2.199	PTB	IG less PTB
Werner, 2013 [26]	RCT (single blinded)	Denmark	Nulliparous pregnant women with an uncomplicated pregnancy, >18 years old, between 27-30 weeks’ gestation	IG 1: Hypnosis IG 2: Relaxation CG: Usual care	IG 1: 493 IG 2: 494 CG: 230 Total: 1.217	PTB, birth weight	No sign differences
Yekefallah, 2021 [27]	Clinical trial study	Iran	Nulliparous pregnant women with an uncomplicated pregnancy, 18-35 years old, between 26-28 weeks’ gestation	IG: Yoga twice a week CG: Usual care	IG: 35 CG: 35 Total: 70	PTB, gestational age, birth weight	IG less PTB, higher gestational age and birth weight

CG, control group; IG, intervention group; LBW, low birth weight; PSRS, Perceived Stress Reactivity Scale; PSS, Perceived Stress Scale; PTB, preterm birth; RCT, randomized controlled trial; STAI, State-Trait Anxiety Inventory.

First, pooled effect sizes for each selected outcome were calculated. The group receiving childbirth training only in the study by Aktan et al. was incorporated as a control group, since this intervention does not primarily target stress [18]. The relaxation group in the study by Werner et al. was incorporated as an intervention in our meta-analysis [26]. This group implemented body awareness, relaxation exercises, and mindfulness techniques, allowing us to assess the effects of these interventions on the PTB rate. The outcomes of the meta-analysis are shown in Figure 2. The incidence of PTB in the intervention group was 6.3%, in comparison to 12.7% in the control group, with a RR of 0.50 (95% CI 0.35 − 0.71, n = 10, I² = 28%, p= <.0001).

Figure 2. Forest plot analysis on stress-reducing interventions and preterm birth risk ratio.

The incidence of LBW was 14.9% in the intervention group, compared to 29.4% in the control group, RR 0.51 (95% CI 0.40 − 0.65, n = 4, I² = 0%, p= <.00001). Results are shown in Figure 3. Mean gestational age was significantly higher in infants born after women participated in stress-reducing interventions. Gestational age mean difference was 0.89 weeks (95% CI 0.08 − 1.71, n = 6, I² = 95%, p=.03). Mean birth weight did not significantly differ between the two groups, showing a mean difference of 143.15 grams (95% CI −37.90 − 324.21, n = 7, I² = 92%, p=.12). Results are shown in Supplemental Figures 1 and 2. No studies described adverse perinatal outcomes.

Figure 3. Forest plot analysis on stress-reducing interventions and low birth weight risk ratio.

The funnel plot was asymmetrical, as shown in Figure 4. The asymmetry highlights the potential impact of publication bias, selective reporting and small-study effects. In addition, a significant number of the included studies were categorized as having uncertain or high risk of bias, primarily due to elevated risks in random sequence generation and allocation concealment, shown in Figure 5. Since blinding of participants for stress-reducing interventions is not possible, performance bias was uncertain for all the included studies.

Figure 4. Funnel plot of the included studies.

Figure 5. Risk of bias summary.

Due to the high prevalence of studies investigating the effect of yoga (n = 5; 757 women), we performed an additional analysis focusing on this specific intervention type. This analysis showed that yoga significantly reduced the incidence of PTB and LBW (RR 0.42, 95% CI: 0.21-0.85, RR 0.57, 95% CI 0.41 − 0.81 respectively), results are shown in Supplemental Figures 3 and 4.

Maternal anxiety was assessed in two studies using the State-Trait Anxiety Inventory (STAI) Scale [18,21]. These studies were not pooled in a meta-analysis due to differences in outcome measures, timing of the outcomes, and missing data. Aktan et al. utilized the STAI-2 questionnaire to assess three groups (childbirth program and Pilates, childbirth program alone, and control group) at 32 weeks of gestation, finding similar mean scores among them [18]. Following four weeks of training, the STAI-1 was examined, and the authors discovered that the mean STAI-1 score was significantly lower in women who underwent childbirth training with clinical Pilates (p= <.05). Consonni et al. conducted a study on a multidisciplinary program where maternal anxiety was evaluated using STAI-1 at baseline between 18 and 22 weeks of gestation [21]. They found comparable baseline scores between the intervention group and control group. However, between 36 and 38 weeks of gestation, the STAI-2 scores were significantly lower in the intervention group (p= <.05).

Two studies examined maternal stress using different measures: the PSS and PSRS [19,22]. These studies were not combined in a meta-analysis due to variations in outcome measures, timing of assessments, and incomplete data. Bhartia et al. found similar PSS scores between the intervention and control groups at baseline [19]. However, at 32 weeks of gestation, the intervention group, which practiced yoga, experienced a significant 17.8% decrease in PSS (p< .001), while the control group showed an 8.4% increase (p=.001). In another study by Malhotra et al. the baseline PSRS scores at 15 weeks of gestation were comparable between the groups [22]. After participating in a Baby Care Program that included mindfulness, yoga, music, baby bonding, and education, the intervention group showed a significant reduction in PSRS scores at 35 weeks of gestation. Moreover, the intervention group’s scores were significantly lower compared to the control group (mean score 0.52 versus 2.2, p=.032).

Discussion

Main findings

This systematic review and meta-analysis, which included ten studies comprising a total of 4.816 low-risk pregnant women, examined the impact of five different stress-reducing interventions on overall PTB rates. Our results indicate that stress-reducing interventions significantly reduce the incidence of PTB in a low-risk obstetric population. With a RR for PTB of 0.50 and a narrow 95% CI of 0.35 − 0.71, stress-reducing interventions demonstrated a substantial reduction in the risk of PTB compared to the control group. In addition, stress-reducing intervention showed significantly lower LBW rates, and significantly higher means gestational age. Additional analysis showed that yoga interventions had a particularly significant effect in reducing both PTB and LBW rates.

Strength and limitations

Our study possesses several notable strengths that distinguish it from previous reviews. Firstly, our study fills a gap in the current literature by evaluating the effect of multiple stress-reducing interventions on PTB rates in a low-risk obstetric population, while previous reviews were limited to specific types of stress-reducing interventions, focused on women already in PTL, or women with diagnosed anxiety or depression. Our study incorporated a diverse range of interventions, encompassing various stress-reducing approaches. By including interventions as Pilates, yoga, multidisciplinary stress reduction programs, combination therapy, and hypnosis, we captured a broader spectrum of potential strategies for PTB prevention. Moreover, unlike prior studies, we conducted a comprehensive meta-analysis to assess the effects of interventions on PTB, LBW, mean gestational age, and mean birth weight. Furthermore, we performed an additional ­analysis focusing on studies investigating yoga, leading to a more accurate understanding of the potential effect of yoga on PTB rates.

There are also limitations to this study. Firstly, the diverse nature of the included interventions necessitates caution when interpreting the results. Establishing a precise definition of stress-reducing interventions proved challenging, since some studies advocate for a broader approach, including low-intensity exercise (LIE) and psychoeducation [31,32]. Assessing maternal stress and anxiety as a secondary outcomes presented difficulties due to the variety of measurement tools and the presence of missing data. The analyses for mean gestational age and mean birth weight showed broad CIs, and a high I² values, indicating significant heterogeneity among the included studies. This can be attributed to several factors, including the diverse characteristics of the study population and variations in interventions. In addition, visual inspection of the funnel plot revealed a considerable risk of publication bias, suggesting our results may be overestimated. Multiple studies included in our meta-analysis were low quality and exhibited a high risk of selection bias, including the two studies that carried the largest weight in our analysis [22,23]. Notably, it is important to highlight that these two studies conducted in India exhibited a biased approach to participant randomization, which might be a potential contributor to the significantly higher PTB rates compared to the global incidence [33]. This raises the concern regarding the potential overestimation of the intervention’s effect. When excluding three studies with a high risk of bias, representing a total of 3.046 women, the RR for PTB changed to 0.59 (95% CI 0.30 − 1.16, p=.130) [22,23,25]. Lastly, all included studies in this review investigated overall PTB and did not differentiate between iatrogenic and spontaneous PTB.

A total of five of the included studies were performed in India, representing 1.199 women (24.9% of total study population), of which four investigated the effects of yoga on PTB rates. Across the conducted studies examining the effects of yoga, the intervention methodology was comparable, focusing on Hatha yoga. This variant of yoga comprises Asana (physical postures), Pranayama (breathing techniques), and meditation. It is important to acknowledge the variations in yoga implementation across the included studies, ranging from daily to twice a week, which may introduce uncertainty when considering the implementation of yoga as standardized intervention. We found no association between the frequency of yoga during pregnancy and PTB rates. For example, the RR for PTB was 0.07 (95% CI 0.01 − 0.54) after daily yoga in the study by Pais et al. and 0.88 (95% CI 0.33 − 2.29) after yoga trice a week in the study by Bolanthakodi et al. [20, 24]. Further research is needed to determine the optimal frequency and duration of yoga sessions for maximum effectiveness in reducing PTB rates.

Interpretation

The association between maternal stress and PTB is well-established in literature [15,16,34]. Prolonged and severe maternal stress during pregnancy has shown to disrupt hormonal balance, affect immune function, and potentially trigger inflammatory responses that can lead to PTB [10,11]. Stress-reducing interventions have been identified as potential strategies to improve maternal mental health during pregnancy. Therapeutic interventions such as massage, relaxation and yoga during pregnancy have been shown to reduce anxiety and stress, reduce cortisol levels, and show positive effects on immune and autonomic nervous system function [35–39].

Despite the well-established association between maternal stress and PTB, the relationship between stress-reducing interventions and their impact on PTB rates remains inconclusive. The study by Mooventhan was the first to review the effects of yoga in both normal- and high-risk women [40]. This comprehensive review yielded promising results, indicating that yoga could serve as an effective approach by enhancing both physical and psychological health-related aspects. Notably, their review included only one study addressing the impact of yoga on PTB rates, and this study was also included in our meta-analysis [23]. In a recent systematic review and meta-analysis by Rong et al. the focus shifted to yoga’s influence on delivery outcomes [41]. This study indicated that yoga was associated with higher rates of vaginal delivery, a reduction in delivery duration, as well as decreased incidence of PTB and LBW. Their assessment of PTB rates relied on two studies, both of which were also integrated into our meta-analysis [20,23]. Apart from reviews specifically focusing on yoga, there are studies investigating a broader approach to stress-reduction. For instance, Beddoe et al. conducted a systematic review specifically focusing on the effects of mind-body interventions, such as relaxation, hypnosis, visual imagery, meditation, yoga, and cognitive-behavioral therapies [32]. Their findings provided modest evidence supporting the effectiveness of mind-body interventions, which resulted in reduced maternal anxiety and stress levels and higher birth weights. Unfortunately, this study did not report outcomes regarding PTB rates. The systematic review by Khianman et al. investigated the effects of relaxation therapies such as meditation, massage, yoga, reflexology, breathing exercises, music therapy, and aromatherapy in women already experiencing PTL, as well as a group of women not experiencing PTL [42]. For women not in PTL, relaxation therapy was found to decrease stress and increase birth weight. The review included only one study that investigated PTB rates after relaxation in women with high anxiety-levels. The findings did not reveal any significant differences between the intervention group and control group [36].

This systematic review and meta-analysis underscores the significance of stress-reducing interventions in lowering PTB risk. Notably, the outcomes of our study reveal that yoga in particular exhibits significant improvements in PTB outcomes. In light of our findings, it is not possible to draw definitive conclusions regarding the causative factor underlying yoga’s influence on the reduction of PTB rates. It is unclear whether this impact is primarily attributed to the stress-reduction facet or to the exercise component inherent in yoga practice. Previous research has shown that LIE is associated with a significant reduction in PTB risk and also lowers maternal stress [9,43]. Exploring the intricate interplay between yoga, exercise, and their combined effects could further illuminate the mechanisms underlying these positive outcomes.

This systematic review and meta-analysis presents evidence supporting the effectiveness of stress-reducing interventions in improving pregnancy outcomes and mental health in low-risk pregnant women. Given the low quality and high risk of bias in the included studies, yet promising results, we propose a RCT of high quality to determine the effectiveness of stress-reducing interventions in reducing PTB risk, focusing on iatrogenic and spontaneous PTB risk at various gestational ages.

Data availablity statement

The protocol can be accessed on PROSPERO (Registration number: CRD42020149469). Data can be accessed upon request by e-mailing the corresponding author. The data that support the findings of this study are available in the supplementary material of this article.

Acknowledgements

We thank Dr. J.M. Limpens of the Medical Library, Department of Research Support Amsterdam UMC for assisting in identifying the literature. We thank Dr. R. van Eekelen of the Department of Epidemiology and Data Science Amsterdam UMC for statistical support.

Disclosure statement

The authors report there are no competing interests to declare.

Correction Statement

This article was originally published with errors, which have now been corrected in the online version. Please see Correction (http://dx.doi.org/10.1080/0167482X.2024.2335858)

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.

Notes on contributors

Laura E. Janssen

Laura E. Janssen, She studied Medicine at the VU in Amsterdam, The Netherlands. After receiving her medical degree she started working as a PhD-student, primary focus on maternal cardiovascular health after spontaneous preterm birth and the identification of risk factors of spontaneous preterm birth. Worked as an obstetrical and surgical resident and currently works as an operational manager at Incision.

Adelia A. Gieskes

Adelia A. Gieskes, She studied Medicine at the Catholic University of Leuven, Belgium. After receiving her medical degree she worked for two years as a peripheral doctor not in training at the Gynecology Department in Alkmaar and Enschede, the Netherlands. She currently works at the Gynecology Department of the academic center in Amsterdam (AMC).

Marjolein Kok

Marjolein Kok, She studied Medicine at the University of Amsterdam (UvA), The Netherlands. Finished her PhD in 2008 entitled ‘‘External Cephalic Version’’. She worked as a gynecologist in Amsterdam UMC, location AMC, Amsterdam, The Netherlands until 2021. She currently works on creating a holistic birth center in the Netherlands.

Christianne J. M. de Groot

Christianne J.M. de Groot, She studied Medicine at the University in Leiden, The Netherlands. Finished her PhD in 1995 about Preeclampsia. She currently works as a professor in gynecology in Amsterdam UMC, location AMC, Amsterdam, The Netherlands. Specialized in obstetric high care, pregnancy complications and hypertensive disorders in pregnancy.

Martijn A. Oudijk

Martijn A. Oudijk, He studied Medicine at the University in Utrecht, The Netherlands. Finished his PhD in 2003 entitled ‘‘Fetal tachycardia, diagnosis and treatment’’. He currently works as a professor in gynecology in Amsterdam UMC, location AMC, Amsterdam, The Netherlands. Specialized in preterm birth and cardiac diseases in pregnancy.

Marjon A. de Boer

Marjon A. de Boer, She studied Medicine at the University in Leiden, The Netherlands. Finished her PhD in 2007 entitled ‘‘Molecular aspects of human papillomavirus in cervical cancer’’. Currently she works as a gynecologist in Amsterdam UMC, location AMC, Amsterdam, The Netherlands. Specialized in perinatology, maternal health and preterm birth.