Lower risk of adverse perinatal outcomes in natural versus artificial frozen-thawed embryo transfer cycles: a systematic review and meta-analysis

Obstetric and perinatal outcomes in singleton pregnancies following medicated, stimulated and natural, frozen embryo transfer cycles: an updated systematic review and meta-analysis

Frozen embryo transfer (FET) has been associated with higher risks of hypertensive disorders of pregnancy (HDP), large for gestational age and high birth weight. This systematic review and meta-analysis evaluates obstetric and perinatal outcomes in medicated, stimulated and natural FET cycles. A literature search was performed using MEDLINE, EMBASE, CINAHL and the Cochrane Library database; 152,590 FET cycles were analysed from 31 included studies. Risk ratios (RR) and 95% confidence intervals (CI) were calculated using fixed and random effects models determined by the heterogeneity (I2). There was significantly higher risk of obstetric and perinatal complications, including HDP (RR 1.84, CI:1.48-2.29, I2 87%) and low birth weight (LBW) (RR 1.25, CI:1.12-1.39, I2 57%) following medicated compared to natural FET cycles. A higher risk of HDP (RR 1.50, CI:1.33-1.64, I2 32%) and macrosomia (RR 1.28, CI:1.17-1.40, I2 37%) was noted following medicated compared to stimulated cycles. Natural demonstrated lower risk of HDP (RR 0.77, CI:0.60-0.99, I2 32%), gestational diabetes (RR 0.78, CI:0.68-0.89, I2 43%), LBW (RR 0.78, CI:0.64-0.95, I2 48%) and small for gestational age (RR 0.83, CI:0.70-0.98, I2 12%) than stimulated cycles. These findings indicate that medicated FET cycles convey greater risks of obstetric and perinatal complications than natural or stimulated cycles.

First-trimester uterine artery pulsatility index and preeclampsia risk in pregnancies after artificial frozen embryo transfer: analysis of over 27,000 pregnancies

BACKGROUND

Accumulating evidence indicates that pregnancies after artificial cycle frozen embryo transfer are associated with an increased risk of preeclampsia. Uterine artery Doppler, along with maternal factors and serum biomarkers, is a crucial biomarker for first-trimester preeclampsia screening, aiding in identifying "high-risk" patients. Guidelines strongly recommend administering aspirin (150 mg/d) in these women, owing to robust evidence demonstrating a 62% reduction in the incidence of preeclampsia. Although previous studies suggested lower uterine artery pulsatility index after frozen embryo transfer, no previous studies explored the impact of the type of endometrial preparation in Uterine Artery Doppler or its influence on estimating first-trimester preeclampsia risk.

OBJECTIVE

The study aims to evaluate the possible impact of endometrial preparation for frozen embryo transfer on the uterine artery pulsatility index during the first-trimester preeclampsia screening.

STUDY DESIGN

This is a retrospective single-center study including 27,289 singleton pregnancies (naturally conceived or after assisted reproductive treatment) who underwent the first-trimester ultrasound screening at our University Hospital between January 2010 and May 2023. Overall, 27,289 pregnancies were included: 23,410 naturally conceived and 3879 following assisted reproductive technologies including 391 after ovulation induction and intrauterine insemination, 888 in vitro fertilization and fresh embryo transfer, and 2600 natural or artificial frozen embryo transfer cycles. An analysis of covariance was conducted to assess if there is an association between the uterine artery pulsatility index value and the mode of conception, adjusting for confounding factors (age, weight, smoking, and oocyte donation).

RESULTS

Overall, pregnancies after artificial frozen embryo transfer demonstrated significantly lower first-trimester uterine artery pulsatility index as compared with all other modes of conception in a multivariable regression analysis adjusted for age, weight, smoking, and oocyte donation. The percent difference was 22.6 [confidence interval, CI 95%: 20.6; 24.5] compared to naturally conceived pregnancy, 24.5 [CI 95%: 20.7; 28.1] to ovulation induction or intrauterine insemination, 24.8 [CI 95%: 22.9; 27.6] to fresh embryo transfer and 21.7 [CI 95%: 17.6; 25.5] compared to natural cycle frozen embryo transfer. When calculating the risk for initiating preventive aspirin administration, the number of patients with increased risk (>1/100) who initiated prophylactic aspirin was significantly lower in the artificial cycle frozen embryo transfer group (7.8% vs 16.0% in natural cycle P<.001 vs 11.0% in Fresh embryo transfer P=.01 vs 10.5% in ovulation induction or intrauterine insemination P=.14 vs 9.3% in naturally conceived pregnancy P=.03). Surprisingly although significantly fewer patients were considered at high risk for preeclampsia in the artificial cycle frozen embryo transfer group, analysis of the actual incidence of preeclampsia demonstrated 3 times higher preeclampsia incidence in artificial cycle group 5.3% (122/2284) as compared with naturally conceived 1.4% (321/23,410), ovulation induction and intrauterine insemination 1.3% (5/391) or natural cycle pregnancies 1.6% (5/316) and more than 2 times higher when compared to fresh embryo transfer pregnancies 2.3% (20/888), P<.001.

CONCLUSION

Pregnancies following frozen embryo transfer in artificial cycle are associated with significantly lower uterine artery pulsatility index during first-trimester preeclampsia screening. This results in a significantly lower number of patients being classified as high-risk for developing preeclampsia, despite accumulating evidence that artificial cycles are linked to an increased risk of preeclampsia. Therefore, the first-trimester preeclampsia risk algorithm should be adjusted to accurately assess risk for those patients undergoing artificial cycle frozen embryo transfer, to prevent the undertreatment of patients who are at very high risk of developing preeclampsia and may benefit from prophylactic aspirin.

Live birth rate and perinatal outcomes following sequential embryo transfer in women with recurrent implantation failure undergoing frozen-thawed embryo transfer cycles

BACKGROUND

Sequential embryo transfer (ET) has been used to improve clinical outcomes in patients with recurrent implantation failure (RIF). This study aimed to evaluate whether sequential ET influence the live birth rate and perinatal outcomes of women with RIF.

METHODS

A cohort study of RIF patients who underwent sequential ET (Seq-ET) during frozen-thawed embryo transfer (FET) cycles between January 2020 and June 2023 was performed. FET patients who underwent double cleavage-stage ET (D3-dET) and double blastocyst ET (D5/6-dET) during the same period composed the control group. The live birth rate and perinatal outcomes of the groups were analyzed and compared.

RESULTS

The Seq-ET group had a significantly greater live birth rate (42.9%) than the D3-dET group (33.1%), and the live birth rate of the Seq-ET group was comparable to that of the D5/6-dET group (35.7%). Female BMI (aOR 0.96, 95%CI 0.92-1.00), stimulation for endometrial preparation (aOR 0.47, 95%CI 0.26-0.84), and endometrial thickness (aOR 1.08, 95%CI 1.00-1.16) were contributing factors to the live birth rate. No statistically significant differences were found in the rate of healthy birth or twins among the Seq-ET, D3-dET and D5/6-dET groups. There was no statistically significant difference in the rates of preterm delivery, birth weight or length, low birthweight, macrosomia, small for gestational age (SGA), gestational diabetes mellitus (GDM), gestational hypertensive disease (GHD), or the sex ratio among the three groups. The infants born in D5/6-dET group had less gestational weeks than in the Seq-ET and D3-dET groups (38.05 ± 1.88 vs. 38.43 ± 2.09 and 38.45 ± 1.80, P = 0. 013) and had a higher risk of large for gestational age (LGA) (aOR 2.15, 95%CI 1.00-4.62) compared to infants born in the D3-dET group.

CONCLUSION

The live birth rate was significantly higher in the Seq-ET group compared with the D3-dET group, and slightly higher compared to the D5/6-dET group. Our results suggested sequential ET did not affect the perinatal outcomes.

Risk assessment of hypertensive disorders of pregnancy and other adverse pregnancy outcomes after frozen embryo transfers following an artificial cycle: A retrospective cohort study

OBJECTIVES

The primary aim was to investigate if frozen embryo transfer (FET) without a corpus luteum increases the risk of hypertensive disorders of pregnancy (HDP). The secondary aim was to investigate other adverse maternal and perinatal outcomes.

METHODS

This was a retrospective cohort study of 1168 singleton pregnancies and live births following a FET with either an artificial cycle (AC-FET) (n = 631) or a natural/modified natural/stimulated cycle (CL-FET) (n = 537) between 2012 and 2020. The data were collected from patient records. The primary outcome was HDP. Secondary outcomes included cesarean sections, placental retention problems, postpartum hemorrhage (PPH), the duration of pregnancy, birth weight, low birth weight, macrosomia, length of gestation, preterm birth, small for gestational age, and large for gestational age.

RESULTS

In the AC-FET group, there was an increased incidence of pre-eclampsia, gestational hypertension, cesarean sections, PPH over 500 and 1000 mL, and retained placental tissue, compared with the CL-FET group. These associations remained significant in logistic regression analyses with clinically relevant adjustments.

CONCLUSION

The risk of HDP and several other maternal complications seems to be increased after AC-FET compared with CL-FET. Our findings support most earlier studies regarding HDP and add to the knowledge on other maternal and perinatal risks involved in AC-FET, including an increased risk of milder forms of placental retention. More studies are needed to confirm these findings.

Progesterone-modified natural cycle preparation for frozen embryo transfer

RESEARCH QUESTION

Is there any difference in clinical outcomes between the progesterone-modified natural cycle (P4mNC) and hormone replacement therapy (HRT) endometrial preparation protocols after single euploid blastocyst frozen embryo transfer (FET) cycles?

DESIGN

A retrospective cohort study was performed at a single, private, high-volume fertility centre. Patients who underwent single euploid blastocyst FET between January 2017 and December 2019 were included. A total of 1933 FET cycles were reviewed, and 723 FET cycles from 548 patients met the inclusion criteria. Two groups were compared according to endometrial preparation: 327 P4mNC-FET and 396 HRT-FET cycles. The primary outcome was the live birth rate. The secondary outcomes included the clinical pregnancy rate and the miscarriage rate.

RESULTS

There were no differences in the clinical pregnancy rate (50.2% versus 47.0%, P = 0.688), miscarriage rate (9.8% versus 14.5%, P = 0.115) and live birth rate (45.0% versus 39.6%, P = 0.331) between the P4mNC-FET and HRT-FET groups after covariate adjustments.

CONCLUSIONS

There were no differences in the clinical outcomes between the P4mNC-FET and HRT-FET cycles. These results indicate that P4mNC-FET cycles produce clinical outcomes comparable to those of more traditional HRT-FET while allowing greater flexibility in the timing of embryo transfer.

Differences in perinatal complications and serum hormone levels due to uterine endometrial preparation methods in frozen-thawed embryo transfer

AIM

In frozen-thawed embryo transfer (FET), differences in endometrial preparation methods affect the incidence of perinatal complications. However, the underlying causes are unclear. We aimed to investigate whether serum E2, P4 levels are associated with perinatal complications.

METHODS

This is a retrospective cohort study, involving 306 successful FET pregnancies from 2017 to 2022. Participants were divided into Natural Cycle (NC) and Hormone Replacement Cycle (HRC) group. We compared serum hormone levels, maternal backgrounds, and perinatal outcomes and complications. Furthermore, within the HRC group, serum hormone levels were compared for perinatal complications previously reported to show differences in incidence rates depending on the method of endometrial preparation.

RESULTS

HRC exhibited significantly higher serum E2 levels during the implantation period, but lower P4 levels during ovulation, implantation, and pregnancy test period compared with NC. HRC also had significantly higher rates of postpartum hemorrhage (PPH) and placenta accreta spectrum (PAS). There was no association found between perinatal complications more likely to occur in HRC and serum E2, P4 levels.

CONCLUSIONS

In HRC, there were more occurrences of PPH and PAS. Although serum E2, P4 levels during FET did not correlate with perinatal complications.

Progesterone concentrations on blastocyst transfer day in modified natural cycle frozen embryo transfer cycles

RESEARCH QUESTION

Are serum progesterone concentrations on the day of modified natural cycle (mNC) frozen blastocyst transfer (FET) without luteal phase support (LPS) associated with clinical pregnancy rate (CPR)?

DESIGN

Data were collected between January 2019 and October 2022 as a sub-study of an ongoing randomized controlled trial assessing pregnancy outcomes in mNC-FET. The sub-study included all women (n = 209) randomized to mNC-FET without LPS at the time of data extraction. Participants were aged 18-41 years, had regular menstrual cycles and underwent mNC-FET treatment with single-blastocyst transfer. Associations between the serum progesterone concentration on the day of blastocyst transfer and CPR, pregnancy rate and pregnancy loss rate (PLR) were examined between groups with low and higher progesterone concentrations using the 25th and 10th percentiles as cut-offs. Multivariate logistic regression analyses were performed to adjust for potential confounding factors.

RESULTS

Progesterone concentrations on the day of blastocyst transfer in mNC-FET without LPS ranged from 4.9 to 91.8 nmol/l, with the 25th and 10th percentiles at 29.0 nmol/l and 22.5 nmol/l, respectively. Serum progesterone concentrations did not differ between women with or without a clinical pregnancy (mean [SD] 38.5 [14.0] versus 36.8 [12.4] nmol/l; P = 0.350). Furthermore, the CPR, pregancy rate and PLR were similar in women with low or high progesterone concentrations when using the 25th or the 10th progesterone percentile as cut-off. Multivariate regression analyses showed no association between progesterone concentrations and CPR.

CONCLUSIONS

No association was found between progesterone concentration on the day of blastocyst transfer and pregnancy outcome in women undergoing mNC-FET without progesterone LPS.

Clinical features of preeclampsia and hypertensive disorders in pregnancies after different frozen embryo transfer regimens

OBJECTIVES

To compare whether the clinical features of preeclampsia (PE) or gestational hypertension (GH) were different in pregnancies after a frozen embryo transfer (FET), depending on the FET regimen used.

STUDY DESIGN

A retrospective study including 58 pregnancies with PE and 64 pregnancies with GH, all with singleton live births. Pregnancies were stratified according to the presence or absence of a corpus luteum (CL).

MAIN OUTCOME MEASURES

Clinical characteristics of PE and GH, maternal background factors, postpartum hemorrhage (PPH), key perinatal outcomes.

RESULTS

Among PE patients, no difference was found in the clinical characteristics and in the maternal background factors, when comparing women with a CL to women without a CL. PE patients in the group without a CL had a hemorrhage of > 500 mL or > 1000 mL significantly more often than patients with a CL. Multivariable analyses confirmed this risk. Perinatal outcomes were similar. Among GH patients, there was no difference in the clinical features and maternal background factors, when comparing CL cycles to cycles without a CL. The amount of PPH was higher among the patients without a CL, but the frequency of a > 500 mL or > 1000 mL hemorrhage was similar between groups. No risk increase was seen in multivariable analyses.

CONCLUSIONS

Among FET patients with PE, the risk of PPH wasincreased in pregnancies after cycles without a CL, compared to cycles with a CL. The presence or absence of a CL did noteffectthe severity of PE and GH, the duration of pregnancy or blood pressure levels.

Current understanding of the pathogenesis of placenta accreta spectrum disorder with focus on mitochondrial function

AIM

The refinement of assisted reproductive technology, including the development of cryopreservation techniques (vitrification) and ovarian stimulation protocols, makes frozen embryo transfer (FET) an alternative to fresh ET and has contributed to the success of assisted reproductive technology. Compared with fresh ET cycles, FET cycles were associated with better in vitro fertilization outcomes; however, the occurrence of pregnancy-induced hypertension, preeclampsia, and placenta accreta spectrum (PAS) was higher in FET cycles. PAS has been increasing steadily in incidence as a life-threatening condition along with cesarean rates worldwide. In this review, we summarize the current understanding of the pathogenesis of PAS and discuss future research directions.

METHODS

A literature search was performed in the PubMed and Google Scholar databases.

RESULTS

Risk factors associated with PAS incidence include a primary defect of the decidua basalis or scar dehiscence, aberrant vascular remodeling, and abnormally invasive trophoblasts, or a combination thereof. Freezing, thawing, and hormone replacement manipulations have been shown to affect multiple cellular pathways, including cell proliferation, invasion, epithelial-to-mesenchymal transition (EMT), and mitochondrial function. Molecules involved in abnormal migration and EMT of extravillous trophoblast cells are beginning to be identified in PAS placentas. Many of these molecules were also found to be involved in mitochondrial biogenesis and dynamics.

CONCLUSION

The etiology of PAS may be a multifactorial genesis with intrinsic predisposition (e.g., placental abnormalities) and certain environmental factors (e.g., defective decidua) as triggers for its development. A distinctive feature of this review is its focus on the potential factors linking mitochondrial function to PAS development.

Ideal frozen embryo transfer regime

PURPOSE OF REVIEW

This review aims to compare evidence on four criteria (embryo implantation, obstetric outcomes, patient convenience, and IVF-unit efficiency) by analyzing published research on different endometrial preparation methods for frozen embryo transfer (FET).

RECENT FINDINGS

While the artificial-FET cycle provides advantages in scheduling and implantation, it falls short in ensuring optimal obstetric outcomes. In contrast, natural-FET ensures embryo implantation conditions if ovulation is correctly identified. Supplementing with exogenous progesterone shields against low corpus luteum progesterone secretion, crucial for positive obstetric outcomes. In mNC-FET, ovulation is hCG-triggered, closely resembling natural cycles and reducing monitoring visits for enhanced patient convenience.Letrozole is a recommended option for anovulatory patients, preserving endometrial thickness. It is cost-effective, less likely to induce multifollicular development than gonadotropins, and better tolerated.In a novel approach, the natural-proliferative-phase-FET initiates progesterone in an unmediated ovulatory cycle at 7 mm endometrial thickness, combining the benefits of a natural proliferative endometrium with the convenience of scheduled artificial cycles.

SUMMARY

The artificial cycle offers scheduling advantages, but may compromise obstetric outcomes. Natural FET relies on accurate ovulation timing for successful implantation. mNC-FET simplifies the process using hCG induction, minimizing clinic visits for improved convenience. Letrozole is highlighted as a cost-effective and well tolerated option in anovulatory patients. A recent innovative approach combines elements of natural and artificial cycles, showing promise for FET procedures.

Assessing obstetric outcomes: A systematic review and meta-analysis comparing fresh, artificial, and natural thaw embryo transfer cycles

BACKGROUND

The increasing utilisation of in vitro fertilisation (IVF) has prompted significant interest in determining the optimal endometrial environment to increase pregnancy rates and minimise the obstetric complications associated with various embryo transfer strategies.

AIMS

To determine which cycle is associated with increased obstetric complications: fresh embryo transfer (FreshET), natural thaw (NatThawET) or artificial thaw (ArtThawET). Outcomes of interest included: hypertensive disorders of pregnancy (HDP), gestational diabetes (GD), pre-term birth (PTB), post-partum haemorrhage (PPH) and large for gestational age (LGA).

MATERIALS AND METHODS

A comprehensive search of MEDLINE, EMBASE, CENTRAL, and PUBMED was conducted from 1947 to May 17, 2022. Two independent reviewers carried out the screening, and data extraction for the following comparisons: ArtThawET vs NatThawET, ArtThawET vs FreshET, and NatThawET vs FreshET. Meta-analysis was conducted using a fixed-effect Mantel-Haenszel model. The quality of the studies was assessed using GRADEpro.

RESULTS

A total of 23 studies were included in this review. ArtThawET was associated with a significantly increased odds of HDP (odds ratio (OR) 1.76, confidence interval (CI) 1.66-1.86), PTB (OR 1.18, CI 1.13-1.23), PPH (OR 2.61, CI 2.3-2.97) and LGA (OR 1.11, CI 1.07-1.15), compared to NatThawET. ArtThawET was also associated with increased odds of HDP (OR 2.13, CI 1.89-2.4), PPH (OR 3.52, CI 3.06-4.04) and LGA (OR 2.12, CI 1.77-2.56), compared to FreshET. Furthermore, NatThawET demonstrated increased odds of HDP (OR 1.20, CI 1.11-1.29), PPH (OR 1.25, CI 1.14-1.38) and LGA (OR 1.85, CI 1.66-2.07) compared to FreshET.

CONCLUSION

When clinically feasible, ArtThawET should be avoided as a first-line option for IVF to reduce the risk of obstetric complications. An adequately powered, multicentre randomised controlled trial is necessary to confirm these findings and investigate the underlying pathophysiology.

Pathologic maternal and neonatal outcomes associated with programmed embryo transfer

PURPOSE

In this first of two companion papers, we critically review the evidence recently published in the primary literature, which addresses adverse maternal and neonatal pregnancy outcomes associated with programmed embryo transfer cycles. We next consider whether these pathological pregnancy outcomes might be attributable to traditional risk factors, unknown parental factors, embryo culture, culture duration, or cryopreservation. Finally, in the second companion article, we explore potential etiologies and suggest strategies for prevention.

METHODS

Comprehensive review of primary literature.

RESULTS

The preponderance of retrospective and prospective observational studies suggests that increased risk for hypertensive disorders of pregnancy (HDP) and preeclampsia in assisted reproduction involving autologous embryo transfer is associated with programmed cycles. For autologous frozen embryo transfer (FET) and singleton live births, the risk of developing HDP and preeclampsia, respectively, was less for true or modified natural and stimulated cycles relative to programmed cycles: OR 0.63 [95% CI (0.57-0.070)] and 0.44 [95% CI (0.40-0.50)]. Though data are limited, the classification of preeclampsia associated with programmed autologous FET was predominantly late-onset or term disease. Other adverse pregnancy outcomes associated with autologous FET, especially programmed cycles, included increased prevalence of large for gestational age infants and macrosomia, as well as higher birth weights. In one large registry study, FET was associated with fetal overgrowth of a symmetrical nature. Postterm birth and placenta accreta not associated with prior cesarean section, uterine surgery, or concurrent placenta previa were also associated with autologous FET, particularly programmed cycles. The heightened risk of these pathologic pregnancy outcomes in programmed autologous FET does not appear to be attributable to traditional risk factors, unknown parental factors, embryo culture, culture duration, or cryopreservation, although the latter may contribute a modest degree of increased risk for fetal overgrowth and perhaps HDP and preeclampsia in FET irrespective of the endometrial preparation.

CONCLUSIONS

Programmed autologous FET is associated with an increased risk of several, seemingly diverse, pathologic pregnancy outcomes including HDP, preeclampsia, fetal overgrowth, postterm birth, and placenta accreta. Though the greater risk for preeclampsia specifically associated with programmed autologous FET appears to be well established, further research is needed to substantiate the limited data currently available suggesting that the classification of preeclampsia involved is predominately late-onset or term. If substantiated, then this knowledge could provide insight into placental pathogenesis, which has been proposed to differ between early- and late-onset or term preeclampsia (see companion paper for a discussion of potential mechanisms). If a higher prevalence of preeclampsia with severe features as suggested by some studies is corroborated in future investigations, then the danger to maternal and fetal/neonatal health is considerably greater with severe disease, thus increasing the urgency to find preventative measures. Presupposing significant overlap of these diverse pathologic pregnancy outcomes within subjects who conceive by programmed embryo transfer, there may be common etiologies.

Pathologic maternal and neonatal outcomes associated with programmed embryo transfer: potential etiologies and strategies for prevention

PURPOSE

In the first of two companion papers, we comprehensively reviewed the recent evidence in the primary literature, which addressed the increased prevalence of hypertensive disorders of pregnancy, late-onset or term preeclampsia, fetal overgrowth, postterm birth, and placenta accreta in women conceiving by in vitro fertilization. The preponderance of evidence implicated frozen embryo transfer cycles and, specifically, those employing programmed endometrial preparations, in the higher risk for these adverse maternal and neonatal pregnancy outcomes. Based upon this critical appraisal of the primary literature, we formulate potential etiologies and suggest strategies for prevention in the second article.

METHODS

Comprehensive review of primary literature.

RESULTS

Presupposing significant overlap of these apparently diverse pathological pregnancy outcomes within subjects who conceive by programmed autologous FET cycles, shared etiologies may be at play. One plausible but clearly provocative explanation is that aberrant decidualization arising from suboptimal endometrial preparation causes greater than normal trophoblast invasion and myometrial spiral artery remodeling. Thus, overly robust placentation produces larger placentas and fetuses that, in turn, lead to overcrowding of villi within the confines of the uterine cavity which encroach upon intervillous spaces precipitating placental ischemia, oxidative and syncytiotrophoblast stress, and, ultimately, late-onset or term preeclampsia. The absence of circulating corpus luteal factors like relaxin in most programmed cycles might further compromise decidualization and exacerbate the maternal endothelial response to deleterious circulating placental products like soluble fms-like tyrosine kinase-1 that mediate disease manifestations. An alternative, but not mutually exclusive, determinant might be a thinner endometrium frequently associated with programmed endometrial preparations, which could conspire with dysregulated decidualization to elicit greater than normal trophoblast invasion and myometrial spiral artery remodeling. In extreme cases, placenta accreta could conceivably arise. Though lower uterine artery resistance and pulsatility indices observed during early pregnancy in programmed embryo transfer cycles are consistent with this initiating event, quantitative analyses of trophoblast invasion and myometrial spiral artery remodeling required to validate the hypothesis have not yet been conducted.

CONCLUSIONS

Endometrial preparation that is not optimal, absent circulating corpus luteal factors, or a combination thereof are attractive etiologies; however, the requisite investigations to prove them have yet to be undertaken. Presuming that in ongoing RCTs, some or all adverse pregnancy outcomes associated with programmed autologous FET are circumvented or mitigated by employing natural or stimulated cycles instead, then for women who can conceive using these regimens, they would be preferable. For the 15% or so of women who require programmed FET, additional research as suggested in this review is needed to elucidate the responsible mechanisms and develop preventative strategies.

Blood pressure and lipid profiles in children born after ART with frozen embryo transfer

STUDY QUESTION

Are blood pressure (BP) and lipid profiles different between children conceived after ART with frozen embryo transfer (FET), fresh embryo transfer (fresh-ET), and natural conception (NC)?

SUMMARY ANSWER

Girls conceived after FET had significantly higher systolic BP and heart rate compared with girls born after fresh-ET; boys conceived after FET had a slightly more favourable lipid profile compared with boys born after fresh-ET and NC.

WHAT IS KNOWN ALREADY

Children conceived after ART with FET are more often born large for gestational age (LGA). LGA in general increases the risk of obesity, diabetes, and cardiovascular disease later in life. Studies on mice and humans on the whole ART population have raised concerns about premature vascular ageing and higher BP. The cardiovascular health of children born after FET is scarcely explored and the results are diverging.

STUDY DESIGN SIZE DURATION

This study was part of the cohort study 'Health in Childhood following Assisted Reproductive Technology' (HiCART), which included 606 singletons (292 boys) born between December 2009 and December 2013: 200 children were conceived after FET; 203 children were conceived after fresh-ET; and 203 children were conceived naturally and matched for birth year and sex. The study period lasted from January 2019 to September 2021.

PARTICIPANTS/MATERIALS SETTING METHODS

The included children were 7-10 years of age at examination and underwent a clinical examination with anthropometric measurements, pubertal staging, and BP measurement. Additionally, a fasting blood sample was collected and analysed for cholesterol, low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides. Systolic and diastolic BP were converted to standard deviation scores (SDS) using an appropriate reference and accounting for height (SDS) of the child. The three study groups were compared pairwise using a univariate linear regression model. Mean differences were adjusted for confounders using multiple linear regression analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Girls and boys conceived after FET had significantly higher birthweight (SDS) compared with naturally conceived peers (mean difference: girls: 0.35, 95% CI (0.06-0.64), boys: 0.35, 95% CI (0.03-0.68)). Girls conceived after FET had significantly higher systolic BP (SDS) and heart rate compared with girls conceived after fresh-ET (adjusted mean difference: systolic BP (SDS): 0.25 SDS, 95% CI (0.03-0.47), heart rate: 4.53, 95% CI (0.94-8.13)). Regarding lipid profile, no significant differences were found between the three groups of girls. For the boys, no significant differences were found for BP and heart rate. Lipid profiles were more favourable in boys born after FET compared with both boys conceived after fresh-ET and NC. All outcomes were adjusted for parity, maternal BMI at early pregnancy, smoking during pregnancy, educational level, birthweight, breastfeeding, child age at examination, and onset of puberty.

LIMITATIONS REASONS FOR CAUTION

The participation rate varied from 18 to 42% in the three groups, and therefore selection bias cannot be excluded. However, extensive non-participant analyses were performed that showed almost no differences in background characteristics between participants and non-participants in the three groups, making selection bias less likely.

WIDER IMPLICATIONS OF THE FINDINGS

The higher birthweight in children conceived after FET was associated with increased systolic BP (SDS) and heart rate in girls conceived after FET compared with fresh-ET. This may be an early indicator of compromised long-term cardiovascular health in this group. The study was not powered to investigate these outcomes and further studies are therefore warranted to confirm the findings.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by the Novo Nordisk Foundation (grant number: NNF18OC0034092, NFF19OC0054340) and Rigshospitalets Forskningsfond. The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov identifier: NCT03719703.

The impact of serum estradiol and progesterone levels during implantation on obstetrical complications and perinatal outcomes in frozen embryo transfer

BACKGROUND

This study sought to evaluate obstetric complications and perinatal outcomes in frozen embryo transfer (FET) using either a natural cycle (NC-FET) or a hormone therapy cycle (HT-FET). Furthermore, we investigated how serum levels of estradiol (E2) and progesterone (P4) on the day of and 3 days after embryo transfer (ET) correlated with clinical outcomes in the two groups.

METHODS

We conducted a retrospective, single-center study from January 1, 2015, to December 31, 2019. The study included couples who underwent NC-FET or HT-FET resulting in a singleton live birth. Serum levels of E2 and P4 were measured on the day of and 3 days after ET. The primary outcomes assessed were preterm birth rate, low birth weight, macrosomia, hypertensive disorders in pregnancy, gestational diabetes mellitus, postpartum hemorrhage, and placenta-related complications.

RESULTS

A total of 229 singletons were included, with 49 in the NC-FET group and 180 in the HT-FET group. There were no significant differences in obstetric complications and perinatal outcomes between the two groups. The NC-FET group had significantly higher serum levels of P4 (17.2 ng/mL vs 8.85 ng/mL; p < 0.0001) but not E2 (144 pg/mL vs 147 pg/mL; p = 0.69) on the day of ET. Additionally, 3 days after ET, the NC-FET group had significantly higher levels of both E2 (171 pg/mL vs 140.5 pg/mL; p = 0.0037) and P4 (27.3 ng/mL vs 11.7 ng/mL; p < 0.0001) compared with the HT-FET group.

CONCLUSION

Our study revealed that although there were significant differences in E2 and P4 levels around implantation between the two groups, there were no significant differences in obstetric complications and perinatal outcomes. Therefore, the hormonal environment around implantation did not appear to be the primary cause of differences in obstetric and perinatal outcomes between the two EM preparation methods used in FET.

Follitropin delta combined with menotropin in patients at risk for poor ovarian response during in vitro fertilization cycles: a prospective controlled clinical study

BACKGROUND

The maximum daily dose of follitropin delta for ovarian stimulation in the first in vitro fertilization cycle is 12 μg (180 IU), according to the algorithm developed by the manufacturer, and based on patient's ovarian reserve and weight. This study aimed to assess whether 150 IU of menotropin combined with follitropin delta improves the response to stimulation in women with serum antimullerian hormone levels less than 2.1 ng/mL.

METHODS

This study involved a prospective intervention group of 44 women who received 12 μg of follitropin delta combined with 150 IU of menotropin from the beginning of stimulation and a retrospective control group of 297 women who received 12 μg of follitropin delta alone during the phase 3 study of this drug. The inclusion and exclusion criteria and other treatment and follow-up protocols in the two groups were similar. The pituitary suppression was achieved by administering a gonadotropin-releasing hormone (GnRH) antagonist. Ovulation triggering with human chorionic gonadotropin or GnRH agonist and the option of transferring fresh embryos or using freeze-all strategy were made according to the risk of developing ovarian hyperstimulation syndrome.

RESULTS

Women who received follitropin delta combined with menotropin had higher estradiol levels on trigger day (2150 pg/mL vs. 1373 pg/mL, p < 0.001), more blastocysts (3.1 vs. 2.4, p = 0.003) and more top-quality blastocysts (1.8 vs. 1.3, p = 0.017). No difference was observed in pregnancy, implantation, miscarriage, and live birth rates after the first embryo transfer. The incidence of ovarian hyperstimulation syndrome did not differ between the groups. However, preventive measures for the syndrome were more frequent in the group using both drugs than in the control group (13.6% vs. 0.6%, p < 0.001).

CONCLUSIONS

In women with serum antimullerian hormone levels less than 2.1 ng/mL, the administration of 150 IU of menotropin combined with 12 μg of follitropin delta improved the ovarian response, making it a valid therapeutic option in situations where ovulation triggering with a GnRH agonist and freeze-all embryos strategy can be used routinely.

TRIAL REGISTRATION

U1111-1247-3260 (Brazilian Register of Clinical Trials, available at https://ensaiosclinicos.gov.br/rg/RBR-2kmyfm ).

Polygenic embryo screening: are there potential maternal and fetal harms?

Polygenic embryo screening (PES) and its derivate the Embryo Health Score (EHS) have generated interest in both infertile and fertile populations due to their potential ability to select embryos with a reduced risk of disease and improved long-term health outcomes. Concerns have been raised regarding the potential harms of IVF itself, including possible epigenetic changes that may affect the health of the offspring in late adulthood, which are not fully captured in the EHS calculation. Knowledge of the potential impacts of the trophectoderm biopsy, which is a key component of the PES procedure, on the offsprings' health is limited by the heterogeneity of the population characteristics used in the published studies. Nonetheless, the literature suggests a possible increased risk of preterm delivery, birth defects and pre-eclampsia after trophectoderm biopsy. Overall, the risks of PES for prenatal and postnatal health remain uncertain, and further research is needed. Counselling patients regarding these risks before considering PES is important, to provide an understanding of the risks and benefits. This review aims to highlight some of these issues, the need for continued investigation in this area, and the importance of informed decision-making in the context of PES.

Natural Cycle Frozen Embryo Transfer: Evaluating Optimal Protocols for Preparation and Timing

Background

While natural cycle frozen embryo transfer (NC-FET) is becoming increasingly common, significant practice variation exists in the use of ovulation induction medications, administration of ovulation trigger, and timing of embryo transfer without consensus as to the optimal protocol.

Aims

The objective of this study is to evaluate the association of key aspects of the NC-FET protocol with implantation, pregnancy and live birth.

Settings and Design

This was a retrospective cohort study of blastocyst stage NC-FET cycles from October 2019 to July 2021 at a single academic fertility centre.

Materials and Methods

Protocols varied between cycles across three key parameters which were evaluated as primary predictors of cycle outcomes: (1) use of letrozole for mild ovarian stimulation/ovulation induction, (2) administration of exogenous ovulation trigger versus spontaneous luteinising hormone surge and (3) transfer timing based on ovulation trigger versus sequential progesterone monitoring. Primary outcomes included implantation rate, clinical pregnancy and ongoing pregnancy.

Statistical Analysis Used

Generalised estimating equations were fitted to obtain adjusted odds ratios or rate ratios as appropriate with 95% confidence intervals for each outcome across the three primary predictors.

Results

A total of 183 cycles from 170 unique patients were eligible for inclusion. The average implantation rate was 0.58, resulting in an overall clinical pregnancy and ongoing pregnancy rate of 59.0% and 51.4%, respectively. After adjusting for age at embryo freeze and history of a failed embryo transfer, there were no significant associations between any predictor and implantation rate, clinical pregnancy, ongoing pregnancy, or live birth.

Conclusion

In NC-FET, a variety of preparation and timing protocols may lead to comparable cycle outcomes, potentially allowing for flexibility on the basis of patient and physician preference. These findings warrant validation in a larger, randomised trial.

Obstetric and neonatal outcomes after natural versus artificial cycle frozen embryo transfer and the role of luteal phase support: a systematic review and meta-analysis

BACKGROUND

The number of frozen embryo transfers (FET) has increased dramatically over the past decade. Based on current evidence, there is no difference in pregnancy rates when natural cycle FET (NC-FET) is compared to artificial cycle FET (AC-FET) in subfertile women. However, NC-FET seems to be associated with lower risk of adverse obstetric and neonatal outcomes compared with AC-FET cycles. Currently, there is no consensus about whether NC-FET needs to be combined with luteal phase support (LPS) or not. The question of how to prepare the endometrium for FET has now gained even more importance and taken the dimension of safety into account as it should not simply be reduced to the basic question of effectiveness.

OBJECTIVE AND RATIONALE

The objective of this project was to determine whether NC-FET, with or without LPS, decreases the risk of adverse obstetric and neonatal outcomes compared with AC-FET.

SEARCH METHODS

A systematic review and meta-analysis was carried out. A literature search was performed using the following databases: CINAHL, EMBASE, and MEDLINE from inception to 10 October 2022. Observational studies, including cohort studies, and registries comparing obstetric and neonatal outcomes between singleton pregnancies after NC-FET and those after AC-FET were sought. Risk of bias was assessed using the ROBINS-I tool. The quality of evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation approach. We calculated pooled odds ratios (ORs), pooled risk differences (RDs), pooled adjusted ORs, and prevalence estimates with 95% CI using a random effect model, while heterogeneity was assessed by the I2.

OUTCOMES

The conducted search identified 2436 studies, 890 duplicates were removed and 1546 studies were screened. Thirty studies (NC-FET n = 56 445; AC-FET n = 57 231) were included, 19 of which used LPS in NC-FET. Birthweight was lower following NC-FET versus AC-FET (mean difference 26.35 g; 95% CI 11.61-41.08, I2 = 63%). Furthermore NC-FET compared to AC-FET resulted in a lower risk of large for gestational age (OR 0.88, 95% 0.83-0.94, I2 = 54%), macrosomia (OR 0.81; 95% CI 0.71-0.93, I2 = 68%), low birthweight (OR 0.81, 95% CI 0.77-0.85, I2 = 41%), early pregnancy loss (OR 0.73; 95% CI 0.61-0.86, I2 = 70%), preterm birth (OR 0.80; 95% CI 0.75-0.85, I2 = 20%), very preterm birth (OR 0.66, 95% CI 0.53-0.84, I2 = 0%), hypertensive disorders of pregnancy (OR 0.60, 95% CI 0.50-0.65, I2 = 61%), pre-eclampsia (OR 0.50; 95% CI 0.42-0.60, I2 = 44%), placenta previa (OR 0.84, 95% CI 0.73-0.97, I2 = 0%), and postpartum hemorrhage (OR 0.43; 95% CI 0.38-0.48, I2 = 53%). Stratified analyses on LPS use in NC-FET suggested that, compared to AC-FET, NC-FET with LPS decreased preterm birth risk, while NC-FET without LPS did not (OR 0.75, 95% CI 0.70-0.81). LPS use did not modify the other outcomes. Heterogeneity varied from low to high, while quality of the evidence was very low to moderate.

WIDER IMPLICATIONS

This study confirms that NC-FET decreases the risk of adverse obstetric and neonatal outcomes compared with AC-FET. We estimate that for each adverse outcome, use of NC-FET may prevent 4 to 22 cases per 1000 women. Consequently, NC-FET should be the preferred treatment in women with ovulatory cycles undergoing FET. Based on very low quality of evidence, the risk of preterm birth be decreased when LPS is used in NC-FET compared to AC-FET. However, because of many uncertainties-the major being the debate about efficacy of the use of LPS-future research is needed on efficacy and safety of LPS and no recommendation can be made about the use of LPS.

Long-term outcomes for children conceived by assisted reproductive technology

Worldwide, more than 10 million children have been born after assisted reproduction technology (ART), comprising up to 7.9% of children born in Europe and up to 5.1 % of children born in the US in 2018. The short-term outcome for children born after ART is well-known from numerous publications, with higher rates of preterm birth and low birth weight in children born after fresh embryo transfer and higher rates of large for gestational age and high birth weight in children born after frozen embryo transfer compared with children born after spontaneous conception. Higher rates of birth defects in children born after ART have also been shown consistently over time. Studies on long-term health outcomes after ART are scarcer but suggest an increased risk of altered blood pressure and cardiovascular function in children born after ART. In this review, we summarize long-term health outcomes in children born after ART and discuss whether the increased health risks are associated with intrinsic maternal or paternal factors related to subfertility or ART treatments per se. Finally, we speculate where the future will bring us regarding ART treatment strategies and the safety of the mother and child.

The influence of embryo stage on obstetric complications and perinatal outcomes following programmed compared to natural frozen-thawed embryo transfer cycles: a systematic review and meta-analysis

Objective

To investigate the effect of embryo stage at the time of transfer on obstetric and perinatal outcomes in programmed frozen-thawed embryo transfer (FET) versus natural FET cycles.

Design

Systematic review and meta-analysis.

Setting

Not applicable.

Patients

Women with programmed frozen-thawed embryo transfer (FET) and natural FET.

Interventions

The PubMed, MEDLINE, and EMBASE databases and the Cochrane Central Register of Controlled Trials (CCRT) were searched from 1983 to October 2022. Twenty-three observational studies were included.

Primary outcome measure

The primary outcomes were hypertensive disorders of pregnancy (HDPs), gestational hypertension and preeclampsia (PE). The secondary outcomes were gestational diabetes mellitus (GDM), placenta previa, postpartum haemorrhage (PPH), placental abruption, preterm premature rupture of membranes (PPROM), large for gestational age (LGA), small for gestational age (SGA), macrosomia, and preterm delivery (PTD).

Results

The risk of HDP (14 studies, odds ratio (OR) 2.17; 95% confidence interval (CI) 1.95-2.41; P<0.00001; I2 = 43%), gestational hypertension (11 studies, OR 1.38; 95% CI 1.15-1.66; P=0.0006; I2 = 19%), PE (12 studies, OR 2.09; 95% CI 1.88-2.32; P<0.00001; I2 = 0%), GDM (20 studies, OR 1.09; 95% CI 1.02-1.17; P=0.02; I2 = 8%), LGA (18 studies, OR 1.11; 95% CI 1.07-1.15; P<0.00001; I2 = 46%), macrosomia (12 studies, OR 1.15; 95% CI 1.07-1.24; P=0.0002; I2 = 31%), PTD (22 studies, OR 1.21; 95% CI 1.15-1.27; P<0.00001; I2 = 49%), placenta previa (17 studies, OR 1.2; 95% CI 1.02-1.41; P=0.03; I2 = 11%), PPROM (9 studies, OR 1.19; 95% CI 1.02-1.39; P=0.02; I2 = 40%), and PPH (12 studies, OR 2.27; 95% CI 2.02-2.55; P <0.00001; I2 = 55%) were increased in programmed FET cycles versus natural FET cycles with overall embryo transfer. Blastocyst transfer had a higher risk of HDP (6 studies, OR 2.48; 95% CI 2.12-2.91; P<0.00001; I2 = 39%), gestational hypertension (5 studies, OR 1.87; 95% CI 1.27-2.75; P=0.002; I2 = 25%), PE (6 studies, OR 2.23; 95% CI 1.93-2.56; P<0.00001; I2 = 0%), GDM (10 studies, OR 1.13; 95% CI 1.04-1.23; P=0.005; I2 = 39%), LGA (6 studies, OR 1.14; 95% CI 1.07-1.21; P<0.0001; I2 = 9%), macrosomia (4 studies, OR 1.15; 95% CI 1.05-1.26; P<0.002; I2 = 68%), PTD (9 studies, OR 1.43; 95% CI 1.31-1.57; P<0.00001; I2 = 22%), PPH (6 studies, OR 1.92; 95% CI 1.46-2.51; P<0.00001; I2 = 55%), and PPROM (4 studies, OR 1.45; 95% CI 1.14-1.83; P=0.002; I2 = 46%) in programmed FET cycles than in natural FET cycles. Cleavage-stage embryo transfers revealed no difference in HDPs (1 study, OR 0.81; 95% CI 0.32-2.02; P=0.65; I2 not applicable), gestational hypertension (2 studies, OR 0.85; 95% CI 0.48-1.51; P=0.59; I2 = 0%), PE (1 study, OR 1.19; 95% CI 0.58-2.42; P=0.64; I2not applicable), GDM (3 study, OR 0.79; 95% CI 0.52-1.20; P=0.27; I2 = 21%), LGA (1 study, OR 1.15; 95% CI 0.62-2.11; P=0.66; I2not applicable), macrosomia (1 study, OR 1.22; 95% CI 0.54-2.77; P=0.64; I2 not applicable), PTD (2 studies, OR 1.05; 95% CI 0.74-1.49; P=0.79; I2 = 0%), PPH (1 study, OR 1.49; 95% CI 0.85-2.62; P=0.17; I2not applicable), or PPROM (2 studies, OR 0.74; 95% CI 0.46-1.21; P=0.23; I2 = 0%) between programmed FET cycles and natural FET cycles.

Conclusions

The risks of HDPs, gestational hypertension, PE, GDM, LGA, macrosomia, SGA, PTD, placenta previa, PPROM, and PPH were increased in programmed FET cycles versus natural FET cycles with overall embryo transfer and blastocyst transfer, but the risks were not clear for cleavage-stage embryo transfer.

The future of frozen-thawed embryo transfer in hormone replacement therapy cycles

PURPOSE OF REVIEW

This review focuses on the efficacy of letrozole stimulated frozen-thawed embryo transfer (FET) compared to hormone replacement therapy (HRT) FET in women with polycystic ovarian syndrome (PCOS) and/or oligo-anovulation. Further, obstetric and perinatal risks in HRT FET are summarized.

RECENT FINDINGS

The presence of a corpus luteum seems to reduce the risk of pregnancy-related hypertension and preeclampsia after FET. As a natural cycle (NC) FET is not an option for women with oligo-/amenorrhea these women may benefit from FET with mild stimulation compared to HRT FET. The intention of mild stimulation in anovulatory women is to induce (mono) ovulation to mimic the endocrine profiles of the natural cycle and the early pregnancy after natural conception. Mild stimulation by letrozole is patient friendly and cheap compared to gonadotropin stimulated FET and has been increasingly used in recent years. Although the quality of evidence is low, the pregnancy outcomes after letrozole FET seems similar or even better compared to HRT FET in women with PCOS and/or oligo-anovulation.

SUMMARY

Natural and modified NC FET should be used whenever possible to mitigate adverse obstetric and perinatal outcomes after HRT FET. For anovulatory women, whenever ovulation can be induced, we advocate the use of mild stimulation FET to create a corpus luteum awaiting results from RCTs limited to oligo-anovulatory women.

Clinical and laboratory parameters associated with pregnancy outcomes in patients undergoing frozen euploid blastocyst transfer

RESEARCH QUESTION

Which factors impact on clinical pregnancy rate (CPR) and live birth rates (LBR) in euploid frozen embryo transfer (eFET) cycles?

DESIGN

Retrospective observational study including 1660 eFET cycles with 2439 euploid blastocysts, from November 2016 to December 2020. The impact of clinical and laboratory parameters on CPR, biochemical miscarriage rate (BMR), clinical miscarriage rate (CMR) and LBR was evaluated.

RESULTS

CPR per transfer was 63.4%, LBR per transfer 51.6%. CPR and LBR were significantly higher when double embryo transfer (DET) was performed (71.6% versus 57.7%, P < 0.001; 55.2% versus 49.1%, P = 0.016, respectively). However, pregnancy loss was significantly higher in the DET group (28.8% versus 22.8%, P = 0.02). When patients were classified by body mass index (BMI), no differences were observed for CPR, but CMR was lower (P < 0.001) and LBR higher (p = 0.031) for the normal BMI group. The natural cycle protocol revealed lower CMR (P < 0.001) and lower pregnancy loss (P < 0.001); subsequently, higher LBR (57.6%, 48.8%, 45.0%, P = 0.001) compared with hormonal replacement protocol and stimulated cycle. Day of trophectoderm biopsy affected CPR (P < 0.001) and LBR (P < 0.001), yet no differences were observed for BMR, CMR or pregnancy loss. The multivariate analysis showed that day 6/7 embryos had lower probabilities for pregnancy; overweight and obesity had a negative impact on LBR, and natural cycle improved LBR (adjusted odds ratio 1.445, 95% confidence interval 0.519-0.806).

CONCLUSIONS

Day of biopsy affected CPR, while BMI and endometrial preparation protocol were associated with LBR in eFET. DET should be discouraged as it will increase the risk of pregnancy loss. Women with higher BMI should be aware of the higher risk of pregnancy loss and lower LBR even though a euploid blastocyst is transferred.

Donated-embryo pregnancies are associated with increased risk of hypertensive disorders even for young recipients: a retrospective matched-cohort study

OBJECTIVE

To determine whether pregnancies with donated embryos are at a higher risk of complications than the pregnancies from autologous frozen-thawed embryo transfer (FET).

DESIGN

Anonymous, multicenter, comparative, observational, retrospective, matched-cohort study.

SETTING

Six French assisted reproductive technique centers from 2003 to 2018.

PATIENT(S)

Seventy-three singleton pregnancies with donated embryos (exposed) and 136 singleton pregnancies after autologous FET (nonexposed) were matched at 7-8 weeks of gestation (pregnancy date, parity, and women's age) (2:1 ratio, respectively). In accordance with French practices, all women were <44 years old and donated embryos were discarded frozen embryos from other couples.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Percentages of hypertensive disorders of pregnancy (HDPs) with donated embryos versus autologous FET.

RESULT(S)

Groups were comparable (mean age: 34.5 years) and HDPs (24.6% vs. 11.9%) were significantly more frequent among the donated-embryo pregnancies, mostly in its severe forms (17.5% vs. 4.6%). In contrast, their respective isolated hypertension frequencies were comparable (7.0% vs. 7.3%). Multivariate analysis retained increased severe HDP risk with donated embryos (odds ratio 2.08 [95% confidence interval: 1.08-4.02]). No significant effect of endometrial preparation was observed. C-sections were more frequent for donated-embryo pregnancies (47.3% vs. 29.2%). Newborns from embryo donation or autologous FET were comparable for prematurity, birth weight and length, Apgar score, small for gestational age, large for gestational age, neonatal malformations, and sex ratio.

CONCLUSION(S)

Even for young women, the risk of severe HDP was 4 times higher for donated-embryo pregnancies than for autologous-FET pregnancies. The HDP risk must be acknowledged to inform donated-embryo recipients and provide careful pregnancy monitoring.

Ultrasound diagnosis of placental and umbilical cord anomalies in singleton pregnancies resulting from in-vitro fertilization

INTRODUCTION

placental anomalies can affect fetal and maternal outcome due to severe maternal hemorrhage potentially resulting in hysterectomy and cord accident including abruption that can determine fetal damage or death. The aims of our study are to determine if the rate of placental and umbilical cord anomalies are more common in IVF singleton pregnancies compared to spontaneous pregnancies; to evaluate the role of ultrasound in screening for these anomalies and to investigate if oocyte donor fertilization is an additional risk factor for the development of these anomalies.

METHODS

this was a prospective cohort study involving two tertiary centers. Patients with a singleton pregnancy conceived with IVF and patients presenting with a spontaneous conception were recruited between 1^st May 2019 to 31^st March 2021. A total of 634 pregnancies were enrolled in the study. All patients underwent similar antenatal care, which included ultrasound examinations at 11-14, 19-22 and 33-35 weeks. Ultrasound findings of placental and/or umbilical cord abnormalities were recorded using the same protocol for both groups and confirmed after birth.

RESULTS

IVF pregnancies had a significantly higher risk of low-lying placenta, placenta previa, bilobed placenta and velamentous cord insertion (VCI) compared with spontaneous pregnancies. In the heterologous subgroup there was a significant increased incidence of placenta accreta spectrum (PAS) disorders than in spontaneous pregnancies. All these anomalies were identified prenatally on ultrasound imaging and confirmed at birth.

DISCUSSION

IVF pregnancies in general and those resulting from donor oocyte in particular are at higher risk of placental and umbilical cord abnormalities compared to spontaneous pregnancies. These anomalies can be diagnosed accurately at the mid-trimester detailed fetal anomaly scan and our findings support the need for a targeted ultrasound screening of these anomalies in IVF pregnancies.

Risk Factors of Preterm Birth and Low Birth Weight in Singletons Conceived Through Frozen Embryo Transfer: A Retrospective Study

Background

The risks of adverse perinatal outcomes in offspring conceived following frozen-thawed embryo transfer (FET) assisted reproductive technology (ART) are inconsistent. The aim of this study was to analyze the risk factors for preterm birth and low birth weight in singletons after FET.

Methods

386 FET cycles was conducted at the Reproductive Medicine Center of Meizhou People's Hospital. The relationship between clinical characteristics and outcomes (term birth and preterm birth, normal birth weight and low birth weight) was analyzed.

Results

The rate of primary infertility, basal FSH and T levels, gestational age, birth weight, and proportion of male fetuses were significantly different in the preterm and full-term groups. Logistic regression analysis showed that high maternal age (≥35 years) (OR 3.652, 95% CI: 1.683-7.925, P=0.001), primary infertility (OR 2.869, 95% CI: 1.461-5.632, P=0.002), low FSH level (<6.215 mIU/mL) (OR 3.272, 95% CI: 1.743-6.144, P<0.001), and hormone replacement therapy (HRT) method (OR 2.780, 95% CI: 1.088-7.100, P=0.033) may increase risk of preterm birth after FET. Gestational age and birth weight were significantly different in fetuses with low birth weight (<2500g, n=38) and normal birth weight (≥2500g and <4000g, n=333). Logistic regression analysis showed that low basal FSH level (<6.215 mIU/mL) (OR 0.425, 95% CI: 0.209-0.865, P=0.018), and HRT method of endometrial preparation for FET (OR 0.272, 95% CI: 0.079-0.934, P=0.039) may reduce the risk of low birth weight after FET.

Conclusion

High maternal age, primary infertility, low FSH level, HRT method of endometrial preparation for FET, and male fetus may increase risk of preterm birth after FET. In addition, primary infertility, low basal FSH level, and HRT method of endometrial preparation may reduce the risk of low birth weight after FET.

Impact of different endometrial preparation protocols before frozen embryo transfer on pregnancy outcomes: a review

The use of frozen embryo transfer cycles has exponentially increased in the last few years. Optimization of endometrial preparation protocols before frozen embryo transfer is mandatory to further improve pregnancy outcomes. This review will focus on the existing literature with regard to the different available endometrial preparation protocols and their impact on pregnancy outcomes. More specifically, we will focus on programmed, natural, and stimulated frozen embryo transfer cycles. The studies performed on this topic are generally of low quality, and only a few well-performed randomized controlled trials have been published. To date, no strong evidence is available to support the use of 1 preparation method over another in terms of pregnancy outcomes. However, robust data have shown a clearly protective effect of natural frozen embryo transfer cycles against long-term obstetric complications, mainly hypertensive disorders of pregnancy and large for gestational age infants. The introduction of individualized luteal phase support in different endometrial preparation protocols is actually gaining a lot of attention and requires further investigation.

Obstetric outcomes following ovarian hyperstimulation syndrome in IVF - a comparison with uncomplicated fresh and frozen transfer cycles

Background

We aimed to assess the correlation between ovarian hyperstimulation syndrome (OHSS) in the early course of in vitro fertilization (IVF) pregnancies and obstetric outcomes.

Methods

We identified records of patients admitted due to OHSS following IVF treatment at our institution between 2008 and 2020. Cases were included if pregnancy resulted in a live singleton delivery (OHSS group). OHSS cases were matched at a 1:5:5 ratio with live singleton deliveries following IVF with fresh embryo transfer (fresh transfer group) and frozen embryo transfer (FET group), according to maternal age and parity. Computerized files were reviewed, and maternal, obstetric and neonatal outcomes compared.

Results

Overall, 44 OHSS cases were matched with 220 fresh transfer and 220 FET pregnancies. Patient demographics were similar between the groups, including body mass index, smoking and comorbidities. Gestational age at delivery, the rate of preterm births, preeclampsia and cesarean delivery were similar between the groups. Placental abruption occurred in 6.8% of OHSS pregnancies, 1.4% of fresh transfer pregnancies and 0.9% of FET pregnancies (p=0.02). On post-hoc analysis, the rate of placental abruption was significantly higher in OHSS pregnancies, compared with the two other groups, and this maintained significance after adjustment for confounders. Birthweights were 3017 ± 483, 3057 ± 545 and 3213 ± 542 grams in the OHSS, fresh transfer and FET groups, respectively (p=0.004), although the rate of small for gestational age neonates was similar between the groups.

Conclusions

OHSS in the early course of IVF pregnancies is associated with an increased risk of placental abruption.

Maternal and obstetric outcomes are influenced by developmental stage and cryopreservation of transferred embryos after clomiphene citrate-based minimal stimulation IVF

STUDY QUESTION

Is the embryo transfer (ET) method associated with maternal and perinatal outcomes after minimal stimulation IVF using clomiphene citrate (CC)?

SUMMARY ANSWER

The incidence of pregnancy complications and adverse perinatal outcomes was influenced by the developmental stage (cleavage versus blastocyst stages) and cryopreservation (fresh versus vitrified) of the transferred embryos.

WHAT IS KNOWN ALREADY

Pregnancies resulting from IVF are associated with higher risks of adverse perinatal outcomes compared to natural conceptions; therefore, the next focus in reproductive medicine should be to assess whether these increased risks are attributable to IVF. Pregnancy complications and perinatal outcomes should be considered in addition to pregnancy outcomes when selecting the ET method, however, studies that describe the influence of transfer methods on perinatal and maternal outcomes are limited.

STUDY DESIGN, SIZE, DURATION

This study retrospectively analysed a large single-centre cohort. The clinical records of 36 827 women who underwent oocyte retrieval (during a CC-based minimal stimulation cycle) followed by their first ET at the fertility treatment centre between January 2008 and December 2017 were retrospectively analysed. The patients underwent a single fresh cleavage-stage ET (SFCT), single vitrified-warmed cleavage-stage ET (SVCT) or single vitrified-warmed blastocyst transfer (SVBT). This study only included one cycle per patient.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oocyte retrieval was performed following CC-based minimal ovarian stimulation. The embryos were transferred 2–3 days after retrieval or vitrified at the cleavage or blastocyst stage. The vitrified embryos were then warmed and transferred within the natural cycles. Pregnancy complications and perinatal outcomes were stratified according to the transfer methods used. Multivariate logistic regression analysis was performed to evaluate the effect of ET methods on the prevalence of pregnancy complications and congenital anomalies.

MAIN RESULTS AND THE ROLE OF CHANCE

The rates of clinical pregnancy and delivery were significantly different among the groups. We analysed pregnancy complications in 7502 singleton births (SFCT, 3395 cycles; SVCT, 586 cycles; and SVBT, 3521 cycles). Multivariate logistic regression analysis revealed that the adjusted odds ratio (AOR) for hypertensive disorders in pregnancy was significantly lower in the SVBT group than in the SFCT group [AOR, 0.72; 95% CI, 0.56–0.92]. The AOR for low-lying placenta was lower in the SVBT group than in the SFCT group (AOR, 0.34; 95% CI, 0.19–0.60). The AOR for placenta previa was lower in the SVCT and SVBT groups than in the SFCT group (AOR, 0.21; 95% CI, 0.07–0.58 versus AOR, 0.53; 95% CI, 0.38–0.75, respectively). A total of 7460 follow-up data on neonatal outcomes was analysed. The AOR for preterm delivery was lower in the SVBT group than in the SFCT group (AOR, 0.78; 95% CI, 0.64–0.94). The AOR for low birthweight was significantly lower after SVCT and SVBT than after SFCT (AOR, 0.68; 95% CI, 0.46–0.98 versus AOR, 0.57; 95% CI, 0.48–0.66, respectively). The AOR for small for gestational age was lower in the SVCT and SVBT groups than in the SFCT group (AOR, 0.68; 95% CI, 0.46–0.98 versus AOR, 0.44; 95% CI, 0.36–0.55, respectively). The AOR for large for gestational age babies was higher in the SVBT group than in the SFCT group (AOR, 1.88; 95% CI, 1.62–2.18). The incidence of each congenital anomaly was similar among the groups.

LIMITATIONS, REASONS FOR CAUTION

The study data were collected through self-reported parental questionnaires on maternal and neonatal outcomes. Our findings were not compared with the incidence of pregnancy complications and congenital anomalies in natural pregnancies. Furthermore, this study was retrospective in nature; therefore, further studies are required to ascertain the generalizability of these findings to other clinics with different protocols and/or different patient demographics.

WIDER IMPLICATIONS OF THE FINDINGS

This study demonstrated reassuring outcomes for SVBT (in terms of a lower incidence of pregnancy complications) compared to SFCT. Our findings provide valuable knowledge that will help improve perinatal and maternal outcomes in CC-based stimulation and inform couples of the possible benefits and risks of each type of ET method.

STUDY FUNDING/COMPETING INTEREST(S)

This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors. The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Optimal Timing of Ovulation Triggering to Achieve Highest Success Rates in Natural Cycles-An Analysis Based on Follicle Size and Oestradiol Concentration in Natural Cycle IVF

INTRODUCTION

Timing of ovulation triggering is essential in infertility treatments including treatments based on natural menstrual cycles. However, data on follicle size and oestradiol (E2) concentration are limited. Therefore, the model of natural cycle IVF (NC-IVF) was applied to provide more detailed information on these parameters to better schedule the optimal time for triggering ovulation.

MATERIALS AND METHODS

A retrospective cross-sectional analysis of 606 monofollicular NC-IVF cycles was performed at a university-based IVF centre from 2016 to 2019. Follicle size and E2 and LH serum concentrations were evaluated on day -5 to 0 (day 0 = day of oocyte retrieval). Ovulation was triggered if follicle size was 14-22 mm. Patients with irregular cycles, endometriosis >II°, cycles with azoospermia or cryptozoospermia and cycles with inconsistent data were excluded. All parameters were analysed inter- and intraindividually, and associations of the parameters were evaluated. Associations were adjusted for age, cause of infertility and number of previous transfers.

RESULTS

The mean age of women undergoing NC-IVF was 35.8 ± 4.0 years. Follicle size increased by 1.04 ± 0.03 mm, and E2 concentration by 167 ± 11.0 pmol/l per day.Based on a multivariate adjusted mixed model with follicle size, E2 and their interaction, the number of retrieved oocytes was associated with E2 concentration (aOR 1.91, 95% CI: 1.03-3.56; p = 0.040). Maturity of oocytes was associated not only with E2 concentration (aOR 2.01, 95% CI: 1.17-3.45; p = 0.011) but also with follicle size (aOR 1.27, 95% CI: 1.01-1.60; p = 0.039), as was the interaction of both parameters (aOR 0.96, 95% CI: 0.93-0.99; p = 0.017).LH surge was calculated to start in 25% of cases at an E2 level of 637 pmol/l, in 50% of cases at 911 pmol/l and in 75% of cases at an E2 level of 1,480 pmol/l.The live birth rate per follicle aspiration cycle was (non-significantly) higher in cycles with follicles sizes at the time of oocyte retrieval of 18-22 mm (7.7%-12.5%) versus in cycles with follicles sizes of 14-17 mm (1.6%-4.3%).

CONCLUSION

The study contributes to an optimization of infertility treatments involving natural cycles. The study gives guidance about the number of days required after follicle monitoring to schedule the optimal time for triggering ovulation.