The impact of supraphysiologic serum estradiol levels on peri-implantation embryo development and early pregnancy outcome following in vitro fertilization cycles

The construction of machine learning-based predictive models for high-quality embryo formation in poor ovarian response patients with progestin-primed ovarian stimulation

OBJECTIVE

To explore the optimal models for predicting the formation of high-quality embryos in Poor Ovarian Response (POR) Patients with Progestin-Primed Ovarian Stimulation (PPOS) using machine learning algorithms.

METHODS

A retrospective analysis was conducted on the clinical data of 4,216 POR cycles who underwent in vitro fertilization (IVF) / intracytoplasmic sperm injection (ICSI) at Sichuan Jinxin Xinan Women and Children's Hospital from January 2015 to December 2021. Based on the presence of high-quality cleavage embryos 72 h post-fertilization, the samples were divided into the high-quality cleavage embryo group (N = 1950) and the non-high-quality cleavage embryo group (N = 2266). Additionally, based on whether high-quality blastocysts were observed following full blastocyst culture, the samples were categorized into the high-quality blastocyst group (N = 124) and the non-high-quality blastocyst group (N = 1800). The factors influencing the formation of high-quality embryos were analyzed using logistic regression. The predictive models based on machine learning methods were constructed and evaluated accordingly.

RESULTS

Differential analysis revealed that there are statistically significant differences in 14 factors between high-quality and non-high-quality cleavage embryos. Logistic regression analysis identified 14 factors as influential in forming high-quality cleavage embryos. In models excluding three variables (retrieved oocytes, MII oocytes, and 2PN fertilized oocytes), the XGBoost model performed slightly better (AUC = 0.672, 95% CI = 0.636-0.708). Conversely, in models including these three variables, the Random Forest model exhibited the best performance (AUC = 0.788, 95% CI = 0.759-0.818). In the analysis of high-quality blastocysts, significant differences were found in 17 factors. Logistic regression analysis indicated that 13 factors influence the formation of high-quality blastocysts. Including these variables in the predictive model, the XGBoost model showed the highest performance (AUC = 0.813, 95% CI = 0.741-0.884).

CONCLUSION

We developed a predictive model for the formation of high-quality embryos using machine learning methods for patients with POR undergoing treatment with the PPOS protocol. This model can help infertility patients better understand the likelihood of forming high-quality embryos following treatment and help clinicians better understand and predict treatment outcomes, thus facilitating more targeted and effective interventions.

High estradiol levels in fresh embryo transfer cycles are not associated with detrimental impact on birth outcomes

PURPOSE

There is an unclear relationship between estradiol levels and fresh embryo transfer (ET) outcomes. We determined the relationship between estradiol on the day of trigger, in fresh ET cycles without premature progesterone elevation, and good birth outcomes (GBO).

METHODS

We identified autologous fresh ET cycles from 2015 to 2021 at multiple clinics in the USA. Patients with recurrent pregnancy loss, uterine factor, and elevated progesterone on the day of trigger (progesterone > 2 ng/mL or 3-day area under the curve > 4.5 ng/mL) were excluded. The primary outcome was GBO (singleton, term, live birth with appropriate weight). Log-binomial generalized estimating equations determined the likelihood of outcomes.

RESULTS

Of 17,608 fresh ET cycles, 5025 (29%) yielded GBO. Cycles with estradiol ≥ 4000 pg/mL had a greater likelihood of GBO compared to cycles < 1000 pg/mL (aRR = 1.32, 95% CI 1.13-1.54). Pairwise comparisons of estradiol between < 1000 pg/mL versus 1000-1999 pg/mL and 1000-1999 pg/mL versus 2000-2999 pg/mL revealed a higher likelihood of GBO with higher estradiol (aRR 0.83, 95% CI 0.73-0.95; aRR 0.91, 95% CI 0.85-0.97, respectively). Comparisons amongst more elevated estradiol levels revealed that the likelihood of GBO remained similar between groups (2000-2999 pg/mL versus 3000-3999 pg/mL, aRR 1.04, 95% CI 0.97-1.11; 3000-3999 pg/mL versus ≥ 4000 pg/mL, aRR 0.96, 95% CI 0.9-1.04).

CONCLUSION

In fresh ET cycles, higher estradiol levels were associated with an increased prevalence of GBO until estradiol 2000-2999 pg/mL, thereafter plateauing. In fresh ET candidates, elevated estradiol levels should not preclude eligibility though premature progesterone rise, and risk of ovarian hyperstimulation syndrome must still be considered.

The pathophysiological role of estrogens in the initial stages of pregnancy: molecular mechanisms and clinical implications for pregnancy outcome from the periconceptional period to end of the first trimester

BACKGROUND

Estrogens regulate disparate female physiological processes, thus ensuring reproduction. Altered estrogen levels and signaling have been associated with increased risks of pregnancy failure and complications, including hypertensive disorders and low birthweight babies. However, the role of estrogens in the periconceptional period and early pregnancy is still understudied.

OBJECTIVE AND RATIONALE

This review aims to summarize the current evidence on the role of maternal estrogens during the periconceptional period and the first trimester of pregnancies conceived naturally and following ART. Detailed molecular mechanisms and related clinical impacts are extensively described.

SEARCH METHODS

Data for this narrative review were independently identified by seven researchers on Pubmed and Embase databases. The following keywords were selected: 'estrogens' OR 'estrogen level(s)' OR 'serum estradiol' OR 'estradiol/estrogen concentration', AND 'early pregnancy' OR 'first trimester of pregnancy' OR 'preconceptional period' OR 'ART' OR 'In Vitro Fertilization (IVF)' OR 'Embryo Transfer' OR 'Frozen Embryo Transfer' OR 'oocyte donation' OR 'egg donation' OR 'miscarriage' OR 'pregnancy outcome' OR 'endometrium'.

OUTCOMES

During the periconceptional period (defined here as the critical time window starting 1 month before conception), estrogens play a crucial role in endometrial receptivity, through the activation of paracrine/autocrine signaling. A derailed estrogenic milieu within this period seems to be detrimental both in natural and ART-conceived pregnancies. Low estrogen levels are associated with non-conception cycles in natural pregnancies. On the other hand, excessive supraphysiologic estrogen concentrations at time of the LH peak correlate with lower live birth rates and higher risks of pregnancy complications. In early pregnancy, estrogen plays a massive role in placentation mainly by modulating angiogenic factor expression-and in the development of an immune-tolerant uterine micro-environment by remodeling the function of uterine natural killer and T-helper cells. Lower estrogen levels are thought to trigger abnormal placentation in naturally conceived pregnancies, whereas an estrogen excess seems to worsen pregnancy development and outcomes.

WIDER IMPLICATIONS

Most current evidence available endorses a relation between periconceptional and first trimester estrogen levels and pregnancy outcomes, further depicting an optimal concentration range to optimize pregnancy success. However, how estrogens co-operate with other factors in order to maintain a fine balance between local tolerance towards the developing fetus and immune responses to pathogens remains elusive. Further studies are highly warranted, also aiming to identify the determinants of estrogen response and biomarkers for personalized estrogen administration regimens in ART.

Estradiol on trigger day: Irrelevant to live birth rates of fresh cycles but positively associated with cumulative live birth rates

OBJECTIVE

To assess the effects of estradiol (E2) on trigger day on cumulative live birth rates (CLBRs), and pregnancy outcomes after fresh and frozen-thawed embryo transfer (FET).

METHODS

This multicenter retrospective cohort study included 42 315 patients from five reproductive centers. Six subgroups were divided according to E2 on trigger day (<1000, 1000-2000, 2000-3000, 3000-4000, 4000-5000, >5000 pg/mL). Smooth curve fitting and nonlinear mixed-effects models were used.

RESULTS

When E2 was <5500 pg/mL, the CLBR increased by 10% for every 1000 pg/mL increase in E2. When E2 was between 5500 and 13 281 pg/mL, CLBR increased by 1.8% for every 1000 pg/mL increase in E2. When E2 was >13 281 pg/mL, CLBR decreased by 3% for every 1000 pg/mL increase in E2. From group E2 < 1000 to group E2 > 5000 pg/mL, pregnancy and live birth rates in fresh cycles were not related to E2. The live birth rate after FET was higher in the E2 ≥ 5000 pg/mL group than in the E2 < 1000 pg/mL group (odds ratio [OR] 4.03, and 95% confidence interval [CI] 3.74-4.35; adjusted OR 1.20, 95% CI 1.05-1.37).

CONCLUSION

CLBR is associated with E2 on trigger day in a segmented manner. Pregnancy and live birth rates in fresh cycles were not associated with E2. The live birth rate in FET cycles was highest when E2 ≥ 5000 pg/mL.

Outcomes of frozen embryo transfer in patients with and without ovarian hyperstimulation syndrome

"Introduction: One of the methods utilized to treat infertility is the use of frozen embryos. This technique is particularly employed in patients with ovarian hyperstimulation syndrome (OHSS), which leads to heightened blood estrogen levels. The purpose of this study was to compare the percentage of pregnancy and abortion between patients who used the frozen embryo method due to OHSS and others who practiced the same method for other reasons. Materials and Methods: This retrospective, cohort study was conducted on a total of 338 patients who visited in vitro fertilization (IVF) section of Kowsar Hospital of Urmia-Iran to employ the frozen embryo method (May 2013 to December 2015). The patients were classified into two groups, i.e. the OHSS group (N=150) and the non-OHSS group (N=188). Data were obtained and examined by evaluating the files in a questionnaire. Results: The two groups did not differ significantly with regard to their mean age (p = 0.57). There was also no statistically significant difference between the OHSS and non-OHSS groups regarding the quality of frozen embryo transferred (P = 0.17). Also, there was also no statistically significant difference between the two groups in terms of their pregnancy rate (OHSS = 30.0% vs. non-OHSS = 25.0%) and miscarriage rate (OHSS = 31.11% vs. non-OHSS = 24.44%) (p = 0.32 and p = 0.31, respectively). Conclusion: Ovum exposure to high estrogen during ovulation stimulation does not affect embryo implantation and miscarriage in patients with OHSS."

Association between serum estradiol level on day of progesterone start and outcomes from frozen blastocyst transfer cycles utilizing oral estradiol

PURPOSE

Supraphysiologic serum estradiol levels may negatively impact the likelihood of conception and live birth following IVF. The purpose of this study is to determine if there is an association between serum estradiol level on the day of progesterone start and clinical outcomes following programmed frozen blastocyst transfer cycles utilizing oral estradiol.

METHODS

This is a retrospective cohort study at an academic fertility center analyzing 363 patients who underwent their first autologous single (SET) or double frozen embryo transfer (DET) utilizing oral estradiol and resulting in blastocyst transfer from June 1, 2012, to June 30, 2018. Main outcome measures included implantation, clinical pregnancy, live birth, and miscarriage rates. Cycles were stratified by quartile of serum estradiol on the day of progesterone start and separately analyzed for SET cycles only. Poisson and Log binomial regression were used to calculate relative risks (RR) with 95% confidence intervals (CI) for implantation, clinical pregnancy, live birth, and miscarriage with adjustments made for age and BMI.

RESULTS

Cycles with the highest quartile of estradiol (mean 528 pg/mL) were associated with lower risks of implantation (RR 0.66, CI 0.50-0.86), ongoing pregnancy (RR 0.66, CI 0.49-0.88), and live birth (RR 0.70, CI 0.52-0.94) compared with those with the lowest estradiol quartile (mean 212 pg/mL). Similar findings were seen for analyses limited to SETs. There was no significant difference in miscarriage rate or endometrial thickness between groups.

CONCLUSION

High levels of serum estradiol on the day of progesterone start may be detrimental to implantation, pregnancy, and live birth following frozen blastocyst transfer.

The Association Between Serum Estradiol Levels on hCG Trigger Day and Live Birth Rates in Non-PCOS Patients: A Retrospective Cohort Study

OBJECTIVE

To retrospectively analyze the association of serum estradiol (E2) levels on human chorionic gonadotropin (hCG) trigger day and live birth rates (LBRs) in women undergoing fresh embryo transfer and not exhibiting polycystic ovary syndrome.

DESIGN

Retrospective cohort study.

METHODS

Analysis of 13,950 patients who had fresh embryo transfer between December 2013 and December 2019. The main outcome measurement was LBRs. Multivariable regression analysis was performed to investigate associations between E2 levels on the hCG trigger day and LBRs. Stratification analysis was performed to test for effect modification in subgroups. Furthermore, a two-piecewise linear regression model was established to find nonlinear relationships.

RESULTS

Multivariable regression analysis showed a significant association between serum E2 levels on the hCG trigger day and LBRs, adjusting for covariates [relative risk (RR) 1.027, 95% confidence interval (CI) 1.007, 1.049]. Stratification analysis showed that the LBRs were positively associated (RR 1.052, 95% CI 1.004, 1.102) with every 1 ng/ml increase of serum E2 on the hCG trigger day for the subgroup with low antral follicle counts on the trigger day. Specifically, a two-piecewise linear regression model showed that there was a positive association (RR 1.188, 95% CI 1.057, 1.334) between serum E2 and LBR for every increase of 1 ng/ml E2 when the concentration of serum E2 was lower than 2.1 ng/ml. However, there was no significant association (RR 1.002, 95% CI 0.971, 1.032) between E2 levels and LBRs when the concentration of E2 was higher than the 2.1ng/ml inflection point.

CONCLUSIONS

Serum E2 levels on the hCG trigger day were segmentally connected with LBRs.

Progesterone/Oestradiol ratio can Better Predict Intracytoplasmic Sperm Injection Outcomes than Absolute Progesterone Level

Background:

Several parameters were proposed to predict the impact of premature luteinization on intracytoplasmic sperm injection (ICSI) outcomes such as isolated progesterone (P) level, progesterone to oocyte ratio, and progesterone/estradiol ratio (P/E2).

Aim:

The aim of this study is to compare the predictive value of P/E2 ratio and isolated P level on the ovulation triggering day for pregnancy outcomes in fresh GnRH antagonist ICSI cycles.

Settings and Design:

A retrospective cohort study conducted in a university-affiliated in vitro fertilization center between January 2017 and April 2019.

Methods:

The study included women who underwent their first- or second-ranked GnRH antagonist ICSI cycles with day-3 embryo transfer. P/E2 ratio was calculated as (P [ng/mL] × 1000)/E2 (pg/mL). Cutoff values of ≥1.5 ng/ml for high P (HP) and ≥0.55 for HP/E2 ratio were chosen based on the literature.

Statistical Analysis:

A receiver operating curve was performed to detect the predictability of serum P/E2 and P for the ongoing pregnancy rate. First, patients were divided according to either P level (low P < 1.5 ng/mL and HP ≥1.5 ng/mL) or P/E2 ratio (low P/E2 <0.55 and HP/E2 ≥ 0.55). Patients were further divided into four subgroups: (Group A: HP and HP/E2 ratio, Group B: low P and low P/E2 ratio, Group C: HP only, and Group D: HP/E2 only). A multivariate regression analysis models were used to account for the effect of the cycle confounders on the likelihood of pregnancy.

Results:

A total of 402 ICSI cycles were analyzed. The area under the curve was 0.67 and 0.59 for P/E2 and P, respectively. P/E2 showed a significant association with ongoing pregnancy (adjusted odds ratios [aOR]: 0.409, 95% confidence interval [CI] 0.222–0.753, P = 0.004) while HP revealed no significant predictive value (aOR: 0.542, 95% CI 0.284–1.036, P = 0.064) after the multivariate analysis.

Conclusions:

P elevation may not present as an independent predictor for cycle outcomes. P/E2 ratio has a better prognostic value than P alone in predicting pregnancy of GnRH antagonist cycles.

Association between serum oestradiol level on the hCG administration day and neonatal birthweight after IVF-ET among 3659 singleton live births

Oestradiol, an important hormone in follicular development and endometrial receptivity, is closely related to clinical outcomes of fresh in vitro fertilization-embryo transfer (IVF-ET) cycles. A supraphysiologic E2 level is inevitable during controlled ovarian hyper-stimulation (COH), and its effect on the outcome of IVF-ET is controversial. The aim of this retrospective study is to evaluate the association between elevated serum oestradiol (E2) levels on the day of human chorionic gonadotrophin (hCG) administration and neonatal birthweight after IVF-ET cycles. The data of 3659 infertile patients with fresh IVF-ET cycles were analysed retrospectively between August 2009 and February 2017 in First Hospital of Zhengzhou University. Patients were categorized by serum E2 levels on the day of hCG administration into six groups: group 1 (serum E₂ levels ≤ 1000 pg/mL, n = 230), group 2 (serum E2 levels between 1001 and 2000 pg/mL, n = 524), group 3 (serum E₂ levels between 2001 and 3000 pg/mL, n = 783), group 4 (serum E₂ levels between 3001 and 4000 pg/mL, n = 721), group 5 (serum E2 levels between 4001 and 5000 pg/mL, n = 548 ), and group 6 (serum E2 levels > 5000 pg/mL, n = 852). Univariate linear regression was used to evaluate the independent correlation between each factor and outcome index. Multiple logistic regression was used to adjust for confounding factors. The LBW rates were as follows: 3.0% (group 1), 2.9% (group 2), 1.9% (group 3), 2.9% (group 4), 2.9% (group 5), and 2.0% (group 6) (P = 0.629), respectively. There were no statistically significant differences in the incidences of neonatal LBW among the six groups. We did not detect an association between peak serum E2 level during ovarian stimulation and neonatal birthweight after IVF-ET. The results of this retrospective cohort study showed that serum E2 peak levels during ovarian stimulation were not associated with birth weight during IVF cycles. In addition, no association was found between higher E2 levels and increased LBW risk. Our observations suggest that the hyper-oestrogenic milieu during COS does not seem to have adverse effects on the birthweight of offspring after IVF. Although this study provides some reference, the obstetric-related factors were not included due to historical reasons. The impact of the high estrogen environment during COS on the birth weight of IVF offspring still needs future research.

Association between blastocyst morphology and maternal first trimester serum markers in ongoing pregnancies obtained after single fresh blastocyst transfer

OBJECTIVE

Is there an association between blastocyst morphology and maternal first trimester serum markers in In Vitro Fertilization (IVF) pregnancies obtained after fresh single blastocyst transfer?

STUDY DESIGN

This bi-centric retrospective study was conducted between January 2012 and August 2018. We included 122 women aged from 18 to 43 years-old, whose pregnancy progressed at least beyond 13 weeks after a single blastocyst transfer and who participated in the first trimester combined screening test. Day 5 and day 6 blastocysts were evaluated according to Gardner and Schoolcraft classification. Patients were classified into three groups according to blastocysts morphological quality: excellent (≥ 3AA), good (3-6AB, 3-6BA, B2), and medium to poor (3-6BB, 3-6AC, 3-6CA, B1, 3-6CB, 3-6BC). First trimester serum markers were measured in maternal blood between 9 and 11 + 6 gestational weeks. Univariate and multivariate analyses were performed.

RESULTS

Female body mass index, smoking status, type of infertility, geographical origin, anti-mullerian hormone level, ovarian stimulation characteristics, pregnancy outcomes and obstetrical complications were comparable between the three groups. Patient's age was not distributed evenly across groups, with women in group "Medium to Poor" appearing to be slightly younger than in other groups. There were no significant differences in mean first trimester serum markers between the three groups (PAPP-A: excellent: 1.23 ± 0.59 MoM; good: 1.45 ± 0.71 MoM; medium to poor: 1.22 ± 0.52 MoM; p = 0,20; free beta-HCG: excellent: 1.66 ± 1.38 MoM; good: 1.19 ± 0.76 MoM; medium to poor: 1.81 ± 1.34 MoM; p = 0,12). No significant difference was found either between mean first trimester serum markers and inner cell mass morphology (PAPP-A: grade A: 1.23 ± 0.58 MoM; grade B: 1.26 ± 0.60 MoM; medium to poor: 1.64 ± 0.87 MoM; p = 0,67 ; free beta-HCG: grade A: 1.66 ± 1.36 MoM; grade B: 1.52 ± 1.10 MoM; medium to poor: 1.57 ± 0.39 MoM p = 0,60), trophectoderm cells morphology (PAPP-A: grade A: 1.25 ± 0.63 MoM; grade B: 1.26 ± 0.51 MoM; medium to poor: not comparable; p = 0,66; free beta-HCG: grade A: 1.60 ± 1.34 MoM; grade B: 1.69 ± 1.14 MoM; medium to poor: not comparable; p = 0,25), or blastocoel expansion (PAPP-A: B1: 1.08 ± 0.51MoM; B2: 1.57 ± 0.70 MoM; B3: 1.26 ± 0.61 MoM; B4: 1.28 ± 0.62 MoM; B5: 1.04 ± 0.38 MoM; p = 0,22; free beta-HCG: B1: 2.01 ± 1.88 MoM; B2: 1.07 ± 0.49 MoM; B3: 1.43 ± 0.87 MoM; B4: 1.68 ± 1.28 MoM ; B5: 1.82 ± 2.03 MoM; p = 0,48). After adjustment on potential confounding factors (female age, type of gonadotropin, parity, number of oocytes retrieved and occurrence of ovarian hyperstimulation syndrome), we did not observe any association between PAPP-A or free beta-HCG levels and blastocyst morphology.

CONCLUSION

Our study concluded that first trimester serum markers were not associated with blastocyst morphological characteristics. Although this needs further confirmation, this suggests that blastocyst morphology would not have an impact on placentation. Therefore, these findings are reassuring for couples undergoing IVF and blastocyst transfer.

The effect of low-dose aspirin on the pregnancy rate in frozen-thawed embryo transfer cycles: A randomized clinical trial

Background

The results of previous studies on the effect of low-dose aspirin in frozen-thawed embryo transfer (FET) cycles are limited and controversial.

Objective

To evaluate the effect of low-dose aspirin on the clinical pregnancy in the FET cycles.

Materials and Methods

This study was performed as a randomized clinical trial from May 2018 to February 2019; 128 women who were candidates for the FET were randomly assigned to two groups receiving either 80 mg oral aspirin (n = 64) or no treatment. The primary outcome was clinical pregnancy rate and secondary outcome measures were the implantation rate, miscarriage rate, and endometrial thickness.

Results

The endometrial thickness was lower in patients who received aspirin in comparison to the control group. There were statistically significant differences between the two groups (p = 0.018). Chemical and clinical pregnancy rates and abortion rate was similar in the two groups and there was no statistically significant difference.

Conclusion

The administration of aspirin in FET cycles had no positive effect on the implantation and the chemical and clinical pregnancy rates, which is in accordance with current Cochrane review that does not recommend aspirin administration as a routine in assisted reproductive technology cycles.

Is the probability of pregnancy after ovarian stimulation for IVF associated with serum estradiol levels on the day of triggering final oocyte maturation with hCG? A systematic review and meta-analysis

PURPOSE

The objective of this systematic review and metaanalysis was to examine if the probability of pregnancy after ovarian stimulation for in vitro fertilization (IVF), using GnRH analogues and gonadotrophins is associated with serum estradiol level (Ε₂) on the day of triggering final oocyte maturation with human chorionic gonadotrophin (hCG).

METHODS

Twenty-one studies were eligible for this systematic review, including 19,598 IVF cycles, whereas three studies were eligible for metaanalysis, including 641 IVF cycles. The main outcome measure was achievement of ongoing pregnancy/live birth and, if not available, clinical pregnancy or biochemical pregnancy.

RESULTS

Pooling of data showed no differences in the probability of clinical pregnancy between patients with high and low Ε₂ levels on the day of triggering final oocyte maturation. The pooled effect sizes for the Ε₂ thresholds groups constructed, regarding clinical pregnancy were 2000-3000 pg/mL-OR 0.91, 95% CI 0.55 to 1.50, (fair quality/moderate risk of bias, n = 1 study), 3000-4000 pg/mL-OR 0.89, 95% CI 0.46 to 1.70, (fair quality/moderate risk of bias, n = 1 study, good quality/no information on which to base a judgement about risk of bias n = 2 studies), 4000-5000 pg/mL-OR 0.74, 95% CI 0.37 to 1.49 fair quality/moderate risk of bias, n = 1 study), 5000-6000 pg/mL-OR 0.62, 95% CI 0.19 to 1.98, (fair quality/moderate risk of bias, n = 1 study). In addition, no difference was observed in the probability of ongoing pregnancy for the Ε₂ threshold group of 3000-4000 pg/mL OR 0.85, 95% CI 0.40 to 1.81(good quality/no information on which to base a judgement about risk of bias, n = 1 study).

CONCLUSION

Currently, there is insufficient evidence to support or deny the presence of an association between the probability of pregnancy and serum Ε₂ levels on the day of triggering final oocyte maturation with hCG in women undergoing ovarian stimulation for IVF.

Association between serum estradiol level on the human chorionic gonadotrophin administration day and clinical outcome

BACKGROUND

Estradiol, as an important hormone in follicular development and endometrial receptivity, is closely related to clinical outcomes of fresh in vitro fertilization embryo transfer (IVF-ET) cycles. The aim of this retrospective study was to evaluate the association between elevated serum estradiol (E2) levels on the day of human chorionic gonadotrophin (hCG) administration and IVF-ET pregnancy and birth outcomes.

METHODS

A total of 1771 infertile patients with their first fresh IVF-ET cycles were analyzed retrospectively between January 2011 and January 2016 in Peking University First Hospital. Patients were categorized by serum E2 levels on the day of hCG administration into six groups: group 1 (serum E2 levels ≤ 1000 pg/mL, n = 205), group 2 (serum E2 levels 1001-2000 pg/mL, n = 457), group 3 (serum E2 levels 2001-3000 pg/mL, n = 425), group 4 (serum E2 levels 3001-4000 pg/mL, n = 310), group 5 (serum E2 levels 4001-5000 pg/mL, n = 237), and group 6 (serum E2 levels > 5000 pg/mL, n = 137). The retrieved oocyte and MII oocyte numbers and implantation and clinical pregnancy rates of the groups were compared as the first objective of the study. For the 360 women with singleton births among all patients, the area under the corresponding receiver operating characteristic curve (ROC curve) was calculated to assess the predictive value of the E2 change for the probability of low birth weight (LBW) infants as the second objective.

RESULTS

The retrieved oocyte and MII oocyte numbers and implantation and clinical pregnancy rates gradually increased from groups 1 to 5 but decreased in group 6. The parameters of group 1 were statistically worse than those of the other groups, from group 2 to group 6 (the number of retrieved oocytes, t = 13.096, t = 23.307, t = 23.086, t = 26.376, t = 19.636, P < 0.003; the number of retrieved MII oocytes, t = 10.856, t = 20.868, t = 21.874, t = 23.374, t = 19.092, P < 0.003; the implantation rate, χ = 12.179, χ = 22.239, χ = 23.993, χ = 23.344, χ = 16.758, P < 0.003; the clinical pregnancy rate, χ = 16.415, χ = 28.074, χ = 35.387, χ = 37.025, χ = 24.590, P < 0.003). ROC analysis revealed that when a serum peak E2 of 3148 pg/mL was used to predict LBW.

CONCLUSIONS

The results indicate that serum E2 levels have a concentration-dependent effect on clinical outcomes. The optimal range of the E2 level during a fresh IVF-ET cycle is 1000 to 3148 pg/mL.

The impact of peak estradiol during controlled ovarian stimulation on the cumulative live birth rate of IVF/ICSI in non-PCOS patients

OBJECTIVE

The study aimed to investigate the impact of the peak E2 level during controlled ovarian hyperstimulation (COS) on the cumulative live birth rate (cLBR) in non-PCOS women with normal ovarian reserve.

MATERIALS AND METHODS

Women between 20 and 39 years were included. Donor cycles and patients who never experienced embryo transfer were excluded. Multivariable regression and smooth curve fitting were applied for statistical analysis.

RESULTS

A total of 1141 patients were included. The mean age, basal AFC, peak E2 level, and number of retrieved oocyte were 30.0 ± 3.7 years old, 16.8 ± 6.7, 3911.0 ± 1302.9 pg/ml, and 13.6 ± 5.5, respectively. In the overall population of the cohort, cLBR, miscarriage rate, and preterm birth rate were 66.9%, 7.4%, and 13.7%, respectively. The results of multivariable regression analysis failed to show the impact of peak E2 on the cLBR [OR (95%CI) 0.995 (0.982, 1.009), P = 0.486]. However, the result of smooth curve fitting indicated that when the peak E2 was lower than 2185 pg/ml, the cLBR increased about 12% with 100 pg/ml increasing of the peak E2. When the peak E2 was higher than 6136 pg/ml, the cLBR decreased about 10% with 100 pg/ml increasing of the peak E2.

CONCLUSION

We concluded that the peak E2 level on hCG trigger day is associated with the cLBR in a segmental pattern. There should be an appropriate range of the peak E2 level during COS to achieve a relative best cLBR in non-PCOS patients using stimulating protocol mainly based on GnRH agonist; however, the cutoff value must vary in different centers.

Embryo transfer associated with hormone replacement therapy cycles using assisted reproductive technology increases placenta accreta spectrum

AIM

To evaluate obstetric outcomes in embryo transfer (ET) during estrogen with progestin hormone replacement therapy (HRT) cycles using assisted reproductive technology (ART).

METHODS

Of the 118 singleton pregnancies conceived with ART and delivered between January 2015 and December 2017, we reviewed the data of 87 cases that had information on HRT at the time of ET. Data on pregnancy outcomes included the presence of small for gestational age fetuses, hypertensive disorders of pregnancy, placenta previa (including low-lying placenta), placental abruption and placenta accreta spectrum (including placenta accreta, placenta increta and placenta percreta). We investigated the relationship between HRT cycles and adverse placental outcomes (placenta accreta spectrum, placental abruption, placenta previa, hypertensive disorders of pregnancy and small for gestational age fetuses). We then analyzed the associations that correlated with adverse placental outcomes.

RESULTS

Patients with ET during HRT cycles were more likely to have placenta accreta spectrum. During the study period, 87 out of 118 singleton live births using ART had information on HRT (60 HRT cycles and 27 ovulation cycles). The incidence of placenta accreta spectrum was significantly higher in the HRT cycle group than in the ovulation cycle group (HRT cycle, 31.7% [19 of 60] vs ovulation cycle, 7.4% [2 of 27]; P < 0.01).

CONCLUSION

The obstetric outcomes occurring in pregnancies involving HRT use may differ among ET cycles. ET during HRT cycles were associated with adverse obstetric outcomes due to placenta accreta spectrum. The potential interaction between HRT cycles and adverse placental events is novel and warrants further investigation.

The VEGF and PEDF levels in the follicular fluid of patients co- treated with LETROZOLE and gonadotropins during the stimulation cycle

BACKGROUND

Previous studies have shown that androgens, in addition to serving as precursors for ovarian estrogen synthesis, also have a fundamental role in primate ovarian follicular development by augmentation of FSH receptor expression on granulosa cells. Recent studies have shown that aromatase inhibitor, letrozole, improves ovarian response to FSH in normal and poor responder patients, possibly by increasing intraovarian androgen levels. Studies in mice also showed an effect of letrozole to increase pigment epithelium-derived factor (PEDF) and to lower vascular epithelial growth factor (VEGF), which might be expected to reduce the risk of ovarian hyperstimulation syndrome (OHSS) with stimulation. The aim of this study was to compare the VEGF and PEDF levels in the follicular fluids of normal responders treated with letrozole and gonadotropins during the ovarian stimulation with patients treated with gonadotropins only.

METHODS

A single center, prospective clinical trial. We collected follicular fluid from 26 patients, on a GnRH antagonist protocol, dual triggered with hCG and GnRH agonist. The patients in one group were co-treated with letrozole and gonadotropins during the ovarian stimulation and the patients in the other group were treated with gonadotropins only. VEGF, PEDF, estrogen, progesterone and testosterone levels were measured by ELISA kits.

RESULTS

The age of the patients, the total dose of gonadotropins and the number of oocytes were comparable between the two groups. In the follicular fluid, the estrogen levels (2209 nmol/l vs. 3280 nmol/l, p = 0.02) were significantly decreased, and the testosterone levels (246.5 nmol/l vs. 40.7 nmol/l, p < 0.001) were significantly increased in the letrozole group compared to the gonadotropin only group. The progesterone levels (21.4 μmol/l vs. 17.5 p = NS) were comparable between the two groups. The VEGF levels (2992 pg/ml vs. 1812 pg/ml p = 0.02) were significantly increased and the PEDF levels (9.7 ng/ml vs 17.3 ng/ml p < 0.001) were significantly decreased in the letrozole group.

CONCLUSIONS

Opposite to observations in the mouse, we found that VEGF levels were increased and PEDF levels were decreased in the follicular fluid in patients treated with letrozole during the stimulation cycles. Further investigation is required to determine if patients treated with letrozole during the IVF stimulation protocol are at increased risk for developing OHSS as a result of these findings.

Does ovarian reserve affect outcomes in single ideal blastocyst transfers in women less than 40 years of age?

PURPOSE

There is much debate whether diminished ovarian reserve is purely a quantitative issue, or if quality as determined by pregnancy potential of the ensuing oocytes is also affected. The purpose of this study was to determine whether diminished ovarian reserve, as established by one of three ways described below, affects pregnancy outcomes of women under 40 years old undergoing a single ideal blastocyst transfer.

MATERIALS AND METHODS

This was a retrospective cohort study, including 507 women undergoing an ideal quality single embryo transfer between August 2010 and March 2014. Logistic regression was used to control for age, duration of infertility, parity, body mass index, and smoking status. For analysis, women were stratified for: antral follicle counts (≤ 5 vs. > 5), basal serum FSH levels (< 13 vs. ≥ 13 IU/L), and quartile of total FSH dose required for stimulation.

RESULTS

In stratifying women by antral follicle count (AFC) ≤ 5 vs. > 5, the pregnancy rate (40 vs. 53%, p = 0.04), clinical pregnancy rate (29 vs. 46%, p = 0.02), and live birth rate (13 vs. 43%, p = 0.001) were superior with AFC > 5. Using FSH levels (< 13 vs. ≥ 13 IU/L), the pregnancy rate (50 vs. 31%, p = 0.27), clinical pregnancy rate (40 vs. 13%, p = 0.45), and live birth rate (38 vs. 13%, p = 0.48) were similar. Examining quartiles of FSH stimulation, the pregnancy rates were similar (from lowest to highest: 45, 52, 54, 41%, p = 0.13); however, clinical pregnancy rate (36, 43, 47, 25%, p = 0.003) and live birth rate (32, 38, 44, 20%, p = 0.005) were superior in lower quartiles vs. the highest quartile.

CONCLUSION

Ovarian reserve may affect embryo pregnancy potential and outcomes when measured by AFC and exogenous stimulation but not by basal FSH levels.

Frozen embryo transfer can be performed in the cycle immediately following the freeze-all cycle

PURPOSE

In this study, we investigated whether the time interval between oocyte retrieval and frozen embryo transfer (FET) affected the live birth (LB) rates of human segmented-IVF cycles.

METHOD

A total of 1338 ICSI freeze-all cycles were performed between February 2015 and January 2016, with 1121 FET cycles being retrospectively analyzed. All vitrified-warmed blastocyst transfers were performed in artificial FET cycles, using gonadotropin-releasing hormone (GnRH) agonist downregulation and oral estrogen endometrial preparation. The primary outcome measure was LB. Cycles were investigated in oocyte retrieval-to-FET interval groups of 32-46, 47-61, 62-76, 77-91, and ≥ 92 days, with the 47-61-day group used as the reference group.

RESULTS

There were no significant differences in LB rates between the groups in the overall analysis, as well as, in sub-analyses investigating LB in terms of single blastocyst transfer (SBT), trigger type (GnRH agonist, triggers including hCG), oocyte number (≤ 5 and ≥ 15), and maternal age (> 35 years).

CONCLUSION

The present study showed that it is feasible to perform transfers 36 days after oocyte retrieval and that delaying FET in freeze-all beyond the cycle immediately following oocyte retrieval does not increase LB rates.

Does daily co-administration of letrozole and gonadotropins during ovarian stimulation improve IVF outcome?

BACKGROUND

For the last year we have been treating normal responders with gonadotropins and letrozole during the whole stimulation in order to improve response to FSH by increasing the intrafollicular androgen concentration, and to reduce circulating estrogen concentrations. The aim of this study was to compare the IVF outcome of normal responders treated with letrozole and gonadotropins during ovarian stimulation with patients treated with gonadotropins only.

METHODS

A single centre retrospective cohort study of 174 patients (87 in each group).

RESULTS

The age of the patients was comparable between the groups. Estradiol levels were significantly higher in the control group (6760 pmol/L vs. 2420 pmol/L respectively, p < 0.01), and the number of follicles ≥15 mm at the trigger day was significantly lower in the control group (7.9 vs. 10, p = 0.02). The number of retrieved oocytes (10 vs. 14.5, p < 0.01), MII oocytes (7.9 vs. 11.2, p < 0.01) and blastocysts (2.7 vs. 4.0, p = 0.02) was significantly higher in the study group. We found no significant differences in the cumulative pregnancy outcome between the two groups (65.2% vs 58.3% p = NS).

CONCLUSIONS

We conclude that co-treatment with letrozole improves the IVF outcome in normal responders in terms of increased number of blastocysts obtained without increasing the pregnancy rate or the risk of OHSS.

Effect of elevated estradiol levels on the hCG administration day on IVF pregnancy and birth outcomes in the long GnRH-agonist protocol: analysis of 3393 cycles

INTRODUCTION

This retrospective study aimed to evaluate the association between elevated serum estradiol (E ₂) levels on the human chorionic gonadotrophin (hCG) administration day and in vitro fertilization (IVF) pregnancy and birth outcomes in the long GnRH-agonist protocol.

METHODS

This study analyzed the data of 3393 infertile women who underwent initial fresh IVF. The patients were categorized into high and low E ₂ groups based on their serum E ₂ levels on the hCG day. Pregnancy and birth outcomes were compared.

RESULTS

The implantation rate, clinical pregnancy rate, and live birth rate were all significantly higher in the high E ₂ group than in the low E ₂ group (p < 0.05). The good-quality embryo rate and abortion rate did not significantly differ between the two groups. There were no significant differences in the mode of delivery, gestational age, birth weight, and fetal gender between the two groups. Furthermore, there were no differences in the risk of preterm birth, low birth weight, and fetal malformation between the two groups in 860 single live births. Subgroup analysis of singleton pregnancies in the high E ₂ (E ₂ ≥ 3757 pg/mL) group revealed a significant increase in abortion rate in the age group of ≥37 years.

CONCLUSIONS

Elevated serum E ₂ levels associated with controlled ovarian stimulation did not increase the risks of preterm birth, low birth weight, and fetal malformation. High E ₂ on the hCG day had no detrimental effect on the implantation rate, clinical pregnancy rate, and live birth rate.

Fresh versus frozen: initial transfer or cumulative cycle results: how do we interpret results and design studies?

The way we practice assisted reproductive technology has changed over time. In many ways these changes have been positive as technology has improved, in vitro culture has improved, and embryo selection increasingly allows a single embryo transfer with high success rates and ever smaller multiple birth rates. However, our specialty has often been criticized for not being critical with respect to the acceptance of new technology. Although the outcome of interest seems clear (increasing birth of a healthy baby), the approach can be more complicated; and as there is a de-linking of egg retrieval and ET, and as costs and procedures increase, we should be rigorous about our acceptance of change. This is not to stall change but to encourage the same rigor and questioning of accepted dogma expected in other fields of medicine. An approach based on standard clinical study design to allow appropriate comparisons between patients, and to allow the most comprehensive information for patient counseling, is presented.

Are intracytoplasmic sperm injection and high serum estradiol compounding risk factors for adverse obstetric outcomes in assisted reproductive technology?

OBJECTIVE

To evaluate whether intracytoplasmic sperm injection (ICSI) use and E2 on the final day of assisted reproductive technology (ART) stimulation are associated with adverse obstetric complications related to placentation.

DESIGN

Retrospective cohort study.

SETTING

Large private ART practice.

PATIENT(S)

A total of 383 women who underwent ART resulting in a singleton live birth.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Adverse placental outcomes composed of placenta accreta, placental abruption, placenta previa, intrauterine growth restriction, preeclampsia, gestational hypertension, and small for gestational age infants.

RESULT(S)

Patients with adverse placental outcomes had higher peak serum E2 levels and were three times more likely to have used ICSI. Adverse placental outcomes were associated with increasing E2 (odds ratio 1.36, 95% confidence interval 1.13-1.65) and ICSI (odds ratio 3.86, 95% confidence interval 1.61-9.27). Adverse outcomes increased when E2 was >3,000 pg/mL and continued to increase in a linear fashion until E2 was >5,000 pg/mL. The association of ICSI with adverse outcomes was independent of male factor infertility. Interaction testing suggested the adverse effect of E2 was primarily seen in ICSI cycles, but not in conventional IVF cycles. Estradiol >5,000 pg/mL was associated with adverse placental events in 36% of all ART cycles and 52% of ICSI cycles.

CONCLUSION(S)

ICSI and elevated E2 on the day of hCG trigger were associated with adverse obstetric outcomes related to placentation. The finding of a potential interaction of E2 and ICSI with adverse placental events is novel and warrants further investigation.

Segmented ART - The new era in ART?

Currently up to 4% of infants born in developing countries are conceived through assisted reproductive technology (ART). Even though most of these conceptions occur and progress without complications, ART procedures and processes may increase iatrogenesis through complications in - and after conception. We herein review and discuss the clinically and scientific implications and evidence of iatrogenesis, and show how the evolution in ART technologies and procedures has led to the current presumption that frozen embryo transfer might be a more optimal strategy than fresh embryo transfer, in terms of not only reproduction, but also of maternal and fetal outcomes. There is increasing scientific evidence to support the notion that controlled ovarian stimulation could induce significant changes to the endocrine profile of a reproductive cycle, especially to the reproductively important early luteal phase. These changes may not only have a negative effect on implantation and early placentation, but also on the mother, the fetus, and the infant. The overt consequences of controlled ovarian stimulation include ovarian hyperstimulation syndrome, reduced embryo implantation, increased ectopic pregnancy, and altered placentation and fetal growth. The cumulative scientific evidence from this review suggests that GnRHa trigger in segmented ART might constitute the future routine treatment regimen for IVF patients, providing a safe, effective, and patient friendly treatment.

Maternal hCG concentrations in early IVF pregnancies: associations with number of cells in the Day 2 embryo and oocytes retrieved

STUDY QUESTION

Do number of cells in the transferred cleavage stage embryo and number of oocytes retrieved for IVF influence maternal hCG concentrations in early pregnancies?

SUMMARY ANSWER

Compared with transfer of a 2-cell embryo, transfer of a 4-cell embryo results in higher hCG concentrations on Day 12 after transfer, and more than 20 oocytes retrieved were associated with low hCG concentrations.

WHAT IS KNOWN ALREADY

Maternal hCG concentration in very early pregnancy varies considerably among women, but is likely to be an indicator of time since implantation of the embryo into the endometrium, in addition to number and function of trophoblast cells.

STUDY DESIGN, SIZE, DURATION

We followed 1047 pregnancies after IVF/ICSI from oocyte retrieval until Day 12 after embryo transfer. Women were recruited in Norway during the years 2005-2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Successful pregnancies after transfer of one single embryo that had been cultured for 2 days were included. Maternal hCG was quantified on Day 12 after embryo transfer by chemiluminescence immunoassay, which measures intact hCG and the free β-hCG chain. Information on a successful pregnancy, defined as birth after >16 weeks, was obtained by linkage to the Medical Birth Registry of Norway.

MAIN RESULTS AND THE ROLE OF CHANCE

Transfer of a 4-cell embryo resulted in higher maternal hCG concentrations compared with transfer of a 2-cell embryo (134.8 versus 87.8 IU/l, P < 0.05). A high number of oocytes retrieved (>20) was associated with low hCG concentrations (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The factors studied explain a limited part of the total variation of hCG concentrations in early pregnancy. Although embryo transfer was performed at the same time after fertilization, we do not know the exact time of implantation. A further limitation to our study is that the number of pregnancies after transfer of a 2-cell embryo was small (27 cases).

WIDER IMPLICATIONS OF THE FINDINGS

Number of cells in the transferred embryo and number of oocytes retrieved may influence the conditions and timing for embryo implantation in different ways and thereby influence maternal hCG concentrations. Such knowledge may be important for interpretation of hCG concentrations in early pregnancy.

The association of serum estradiol level with outcomes of clomiphene citrate/human menopausal gonadotropin ovarian stimulation for in vitro fertilization and embryo transfer

BACKGROUND

The purpose of this study was to test the hypothesis that estradiol (E2) level on day 3 may be associated with in vitro fertilization (IVF) outcomes.

METHODS

The records of patients who received clomiphene citrate 100 mg/day plus human menopausal gonadotropin 150 IU/day from day 3 and received frozen-thawed embryo transfers were reviewed. Patients were divided into three groups: group A (E2 ≤30 pg/ml), group B (30< E2 ≤50 pg/ml), and group C (E2 >50 pg/ml). A total of 1080 cycles from 941 patients were included.

RESULTS

The number of eggs and MII oocytes were less in group C than group A (both, P = 0.001). The embryo implantation (P = 0.006) and clinical pregnancy rates (P = 0.036) were lower in group C than group B, and the rates were similar between group A and B.

CONCLUSION

Maintaining the serum E2 level from 30 to 50 pg/ml may result in a higher clinical pregnancy rate in IVF cycles.

Perinatal outcomes after fresh versus vitrified-warmed blastocyst transfer: retrospective analysis

OBJECTIVE

To investigate the possible effect of controlled ovarian stimulation on the perinatal outcomes of assisted reproductive technology pregnancies, by comparing the outcomes from fresh ET with frozen ET (FET) with blastocysts of similar quality.

DESIGN

Retrospective observational study.

SETTING

Private fertility center.

PATIENT(S)

Seven hundred eighty-four fresh transfers and 382 vitrified-warmed double blastocyst transfers.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Miscarriage, perinatal mortality, preterm delivery, live birth, live-birth weights, and gestational age of live births.

RESULT(S)

FET resulted in higher implantation rates (51.5% vs. 40.6%), higher live-birth rates per transfer (56.8% vs. 44.3%), and lower ectopic pregnancy rates (0.32% vs. 1.80%). FET pregnancies also had higher day 14 βhCG levels per implantation (148.2 vs. 176.2 IU/L) and higher infant birth weights (singletons Δ109.4 g, twins Δ124 g). Female infants benefitted the most in terms of birth weight. Miscarriage, premature delivery, perinatal morbidity, and live birth per pregnancy were all nonsignificantly different between fresh ET and FET.

CONCLUSION(S)

Clinically significant differences between the peri-implantation and perinatal outcomes of fresh ET and FET suggest better endometrial receptivity and placentation in FET cycles.

Correlation between follicular fluid 25-OH vitamin D and assisted reproductive outcomes

BACKGROUND

Vitamin D in complex with its receptor by regulating gene expression, endometrium immune response and stimulation of endometrium decidualization can be involved in implantation. So, it seems that the amount of vitamin D in follicular fluids (FF) may have an association with ART success.

OBJECTIVE

First, we intended to investigate the possible association between levels of follicular fluids 25-OH vitamin D with assisted reproductive outcomes. Second, we examined relationship between 25-OH vitamin D levels with number and quality of oocytes.

MATERIALS AND METHODS

In a prospective study, 80 infertile female candidates for IVF/ICSI were enrolled. Blood samples (on the day of human chorionic gonadotropin administration) and follicular fluids were taken, and then levels of serum estradiol and follicular fluids 25-OH vitamin D were measured. Also clinical characteristics of patients (duration of infertility, causes of infertility, menstrual status), number and quality of oocytes, number of fertilized oocytes, estradiol levels, and clinical pregnancy were evaluated.

RESULTS

Concentration of FF 25-OH vitamin D in pregnant women was significantly higher than non-pregnant women (p=0.007) but there were no significant differences in age, body mass index (BMI), duration of infertility, menstrual status, number of oocytes, oocytes quality, number of fertilized oocytes, and serum estradiol levels between the two groups. Statistically positive correlation was found between 25-OH vitamin D levels with patient age and implantation rate (r=0.264, p=0.018 and r=0.301, p=0.007 respectively).

CONCLUSION

The obtained results suggest that vitamin D without affecting the number and quality of oocytes can independently improve implantation rate and IVF outcome.

A physiological, rather than a superovulated, post-implantation environment can attenuate the compromising effect of assisted reproductive techniques on gene expression in developing mice embryos

Assisted reproductive techniques (ARTs) may perturb the pre-/peri-conception microenvironments, which subsequently threaten the health of offspring. This study aimed to investigate the effects of superovulation, vitrification, in vitro culture, and embryo transfer on the expression of epigenetic modulators, imprinted genes, and pluripotency markers in expanded blastocysts and Day-9.5 (D9.5) concepti. Results revealed that 53.4% (8/15) and 86.7% (13/15) of genes in the fetus and placenta, respectively, have similar patterns of transcription in all D9.5 concepti, despite the perturbed mRNA expression observed at the blastocyst stage for each embryo-production technique. These observations indicate a counterbalancing of the abnormal expression pattern analyzed at the blastocyst stage during post-implantation development, particularly when the uterus of a naturally synchronized foster mother is employed. Superovulation resulted in the most abnormal expression patterns compared to other treatment groups, although these same blastocysts were able to develop in a synchronized uterus. Thus, superovulation creates a hormonal environment that negatively affected gene expression and impairs fetal growth more adversely during post-implantation development than other ART protocols, such as in vitro culture, vitrification, or embryo transfer-although each did contribute negatively to the implantation and development process. Together, these results may have implications for treating infertility in humans.

Why we should transfer frozen instead of fresh embryos: the translational rationale

Epidemiologic studies have shown an increased rate of adverse perinatal outcomes, including small for gestational age (SGA) births, in fresh in vitro fertilization (IVF) cycles compared with frozen embryo transfer cycles. This increase is not seen in the donor oocyte population, suggesting that it is the peri-implantation environment created after superovulation that is responsible for these changes. During a fresh IVF cycle, multiple corpora lutea secrete high levels of hormones and other factors that can affect the endometrium and the implanting embryo. In this review, we discuss both animal and human data demonstrating that superovulation has significant effects on the endometrium and embryo. Additionally, potential mechanisms for the adverse effects of gonadotropin stimulation on implantation and placental development are proposed. We think that these data, along with the growing body of epidemiologic evidence, support the proposal that frozen embryo transfer should be considered preferentially, particularly in high responders, as a means to potentially decrease at least some of the adverse perinatal outcomes associated with IVF.