A critical appraisal of studies on endometrial thickness and embryo transfer outcome

Correlation of MicroRNA-31 with Endometrial Receptivity in Patients with Repeated Implantation Failure of In Vitro Fertilization and Embryo Transfer

OBJECTIVE

This trial probed the correlation between miR-31 expression and endometrial receptivity (ER) in patients with repeated implantation failure (RIF) of in vitro fertilization and embryo transfer (IVF-ET).

METHODS

A retrospective study of 80 infertility patients who underwent IVF-ET assisted conception treatment were divided into RIF group and normal pregnancy group (control group) according to the pregnancy outcome after embryo transfer. General information of both groups was collected. Endometrial tissues were collected in the middle luteal phase of the menstrual cycle before IVF-ET. miR-31 levels in endometrial tissues were measured, and endometrial tolerance indicator pulsatility index (PI), resistance index (RI), and endometrial thickness (Em) were detected. The correlation between endometrial miR-31 levels and ER indices was evaluated by Pearson method. ROC curves were utilized to analyze the efficacy of miR-31 in predicting RIF occurrence. The influencing factors of RIF were analyzed by binary Logistic regression.

RESULTS

RIF patients had increased miR-31 expression level and endometrial tolerance indicator PI, and RI while decreased Em (p < 0.05). miR-31 in RIF patients was positively correlated with PI and RI, and negatively correlated with Em (p < 0.05). The area under the curve for miR-31 to predict the occurrence of RIF was 0.899, with a sensitivity of 0.750 and a specificity of 0.950. PI, RI, and miR-31 were risk factors for developing RIF in IVF-ET women, and Em was a protective factor (p < 0.05).

CONCLUSION

miR-31 in RIF patients is positively correlated with PI and RI, and negatively correlated with Em.

Endometrial Infusion with Plasma Rich in Growth Factors (PRGF) in IVF Cycles: Randomized Clinical Trial in Very Thin Endometrium and Observational Uncontrolled Follow-Up After the Randomized Clinical Trial

Objectives: To assess if the instillation of plasma rich growth factors (PRGFs) improves endometrial thickness (EMT) in frozen embryo cycles performed under hormone treatment where the endometrium was very thin (≤5 mm). Methods: First, a randomized controlled trial (RCT) was performed comparing women only receiving an increase in estrogen therapy (n = 9) and women receiving both the increase in estrogen therapy and three instillations of PRGF (n = 13). The second part of the study consisted of a prospective observational follow-up of the patients included in the RCT (for 1-3 months in the study group, and for 1-6 months in the control group). Results: In the RCT, there was an increase in EMT in both the PRGF and control groups. However, the increase was significantly higher in the PRGF group (1.30 ± 0.67 mm) compared to the control group (0.58 ± 0.51 mm). In the PRGF group, 23% achieved an EMT of 7 mm compared to 0% in the control group. There were 2 pregnancies in the PRGF group resulting from the 3 transfers performed in that group. No transfer was carried out in the control group. There was a significant increase in EMT 1-3 months after the PRGF cycle. The live birth rate per transfer was 20% in the cycles following the PRGF cycles, whereas it was 30% per starting woman. For women in the control group who later underwent PRGF, the LBR was 57.1%. Conclusions: PRGF instillation in cases of very thin endometrium increases EMT moderately. It is suggested that the beneficial effect of PRGF may persist for 1-3 cycles after instillation.

Association of endometrial thickness with live birth rates among women undergoing fresh IVF, FET, and PGT cycles

Background

Endometrial thickness (EMT) is a crucial indicator of endometrial receptivity in assisted reproductive technology (ART). However, its relationship with pregnancy outcomes remains unclear, especially across different cycle types such as fresh in vitro fertilization-embryo transfer (IVF-ET), frozen-thawed embryo transfer (FET), and preimplantation genetic testing for aneuploidy embryo transfer (PGT-ET). The clinical significance of EMT and its optimal range for improving ART outcomes remain subjects of debate.

Methods

This retrospective cohort study analyzed data from 80,585 ART cycles conducted between July 2008 and December 2022 at a private reproductive center, including 25,683 fresh IVF-ET, 33,112 FET, and 1,071 PGT-ET cycles. EMT was measured via ultrasound on the day of HCG administration and grouped into ranges for comparison. Primary outcomes included live birth rates (LBR) and clinical pregnancy rates (CPR) across EMT ranges. Statistical analyses, including chi-square tests, receiver operating characteristic (ROC) analysis, and adjusted risk ratio (aRR) calculations, were performed to evaluate the association between EMT and pregnancy outcomes.

Results

The relationship between EMT and LBR was non-linear, with no single cutoff value. LBR varied significantly across EMT ranges, peaking at approximately 12 mm in fresh IVF-ET cycles and around 10 mm in FET and PGT-ET cycles. Higher EMT was generally associated with improved LBR and CPR, but predictive power was limited (AUC: 0.56-0.60). Compared to an EMT of 10-11.9 mm, fresh IVF-ET cycles with EMT <10 mm had significantly lower LBR (aRR: 0.60-0.86), while those with EMT ≥12 mm had higher LBR (aRR: 1.12-1.17). Similar trends were observed in FET and PGT-ET cycles, although sensitivity to EMT variations was lower, particularly in PGT-ET cycles. Miscarriage rates (MR) showed no significant differences across EMT groups.

Conclusion

This study demonstrates that EMT has a non-linear association with LBR and CPR across fresh IVF-ET, FET, and PGT-ET cycles, with no single cutoff value. While higher EMT generally correlates with improved outcomes, its overall predictive value for LBR is limited. The findings underscore the need for individualized evaluation of EMT based on cycle type to optimize reproductive outcomes in ART.

Steps towards the clinical application of endometrial and menstrual fluid mesenchymal stem cells for the treatment of gynecological disorders

INTRODUCTION

The human endometrium is a highly regenerative tissue that contains mesenchymal stem/stromal cells (MSCs). These MSCs are sourced via office-based biopsies and menstrual fluid, providing a less invasive and readily available option for cell-based therapies. This review provides an update on endometrial-derived MSCs as a treatment option for gynecological diseases.

AREAS COVERED

This narrative review covers the characterization and therapeutic mechanisms of endometrium biopsy-derived MSCs (eMSCs) and menstrual fluid-derived mesenchymal stromal cells (MenSCs), highlighting similarities and differences. It also covers studies of their application in preclinical animal models and in clinical trials as potential cell-based therapies for gynecological diseases.

EXPERT OPINION

eMSCs and MenSCs from a homologous tissue source have the potential to promote regenerative activity as a treatment for gynecological diseases. Both eMSCs and MenSCs demonstrate therapeutic benefits through their paracrine activity in tissue regeneration, immunomodulation, angiogenesis, and mitigating fibrosis. Further research is essential to establish standardized isolation and characterization protocols, particularly for heterogeneous MenSCs, and to fully understand their mechanisms of action. Implementing SUSD2 magnetic bead sorting for purifying eMSCs from endometrial tissues and menstrual fluid is crucial for their use in future cell-based therapies. Optimization of production, storage, and delivery methods will maximize their therapeutic effectiveness.

Causes of embryo implantation failure: A systematic review and metaanalysis of procedures to increase embryo implantation potential

Introduction

Infertility is characterized by the failure to conceive after 12 months of unprotected sexual intercourse. In assisted reproduction technologies (ARTs), in-vitro fertilization and embryo transfer (IVF-ET) are pivotal, with the quality of embryo quality essential for successful implantation.

Objective

This systematic review with meta-analysis aimed to explore the prevalence of embryonic factors involved in the implantation process, concentrating on the following research inquiries: 1) the implantation rates of euploid versus untested embryo transfers; 2) the efficiency of transferring good embryos in different age groups; 3) the impact of age on good embryo transfers to gestational carriers; and 4) the transfer of donated gametes/embryos. The goal is to identify critical points in implantation to improve therapies.

Methods

A comprehensive literature search identified 1474 relevant papers, 11 of which met the inclusion criteria. The information was gathered using a standardized form, and the risk of bias was evaluated. A meta-analysis of subgroups to determine euploid embryo transfer efficiency was conducted to synthesize and explore the results. Furthermore, data extracted from registries document the persistent secondary role of extraembryonic determinants in successful implantation.

Results

The meta-analysis demonstrated that preimplantation genetic testing for aneuploidy (PGT-A) significantly increased the odds of implantation. Age was found to influence extraembryonic factors, with older women experiencing reduced embryo implantation as gestational carriers. However, the overall incidence of extraembryonic factors was low. This review highlights the need to focus on PGT-A, diagnostic hysteroscopy, and endometrial receptivity for improving implantation rates.

Conclusion

Implantation success in ARTs largely depends on embryo euploidy. While achieving three euploid embryos greatly increases success rates, it is challenging in older women. Extraembryonic factors, although present, have a marginal impact. Subsequent studies ought to concentrate on modulating endometrial responses immunologically and developing algorithms to improve the precision of predicting implantation success; as well as the timing of endometrial receptivity and the occurrence of dormant embryo phenomena also warrants further investigation.

A Qualitative Exploration of Emotional Experiences in Patients with Thin Endometrium Undergoing Repeated Cancellations of Frozen-Thawed Embryo Transfer Cycles

Objective

The aim of this study was to investigate the emotional experience of patients with thin endometrium (TE) who have repeatedly cancelled their cycles due to unsuitability for embryo implantation during the endometrial preparation phase of freeze-thaw embryo transfer (FET). The overall aim is to improve management strategies and quality of life for these patients.

Methods

A descriptive phenomenological methodology was utilized to conduct in-depth, semi-structured interviews with ten patients diagnosed with TE who had experienced repeated FET cancellations between January and June 2024. The emotional responses elicited were systematically analyzed to identify core themes.

Results

Four primary themes emerged: 1) a spectrum of negative emotional responses; 2) deterioration in marital relationships; 3) a pronounced need for professional support, including a) expanded treatment options and b) informational guidance; and 4) diverse coping mechanisms employed by patients.

Conclusion

Healthcare providers must recognize and address the complex emotional responses associated with repeated transfer cancellations in patients with TE. Tailored psychological interventions and comprehensive support services may not only foster emotional well-being but also potentially improve clinical outcomes in assisted reproductive technology (ART) settings.

Impact of endometrial thickness and its combined effect with maternal age on singleton adverse neonatal outcomes in frozen-thawed embryo transfer cycles

Background

Thin endometrial thickness (EMT) and advanced age are both common risk factors for adverse neonatal outcomes (ANOs). However, studies evaluating the impact of EMT and combined effect of EMT and age on ANOs remain scarce with conflicts.

Method

A retrospective cohort study was conducted on 7,715 singleton deliveries from frozen embryo transfer (FET) cycles between 2017 and 2021. The participants were categorized into four groups based on EMT quartiles (≤8.5, 8.6-9.5, 9.6-10.5, and >10.5 mm). The primary outcome was preterm birth (PTB), and the secondary outcome included early PTB (EPTB), small/large for gestational age (SGA/LGA), and low birth weight (LBW).

Results

Baseline characteristics were unevenly distributed across EMT groups. After adjusting for the confounders, EMT was found to be associated with the incidence of PTB (aOR 0.922, 95% CI 0.874-0.973, p = 0.003), EPTB (aOR 0.795, 95% CI 0.663-0.954, p = 0.014), LBW (aOR 0.886, 95% CI 0.796-0.986, p = 0.027), and LGA (aOR 1.038, 95% CI 1.004-1.074, p = 0.030). Furthermore, the rates of LBW in the group of EMT at 9.6-10.5 mm (aOR 0.551, 95% CI 0.339-0.895, p = 0.016) and >10.5 mm (aOR 0.536, 95% CI 0.332-0.865, p = 0.011) were lower compared to those with EMT ≤8.5 mm. Among women aged over 35, EMT of 9.6-10.5 mm was associated with a significantly lower incidence of LBW compared to thinner EMT, without increasing the risk of ANOs related to thicker EMT.

Conclusions

Our study demonstrated the independent nonlinear impact of EMT on PTB, EPTB, LGA, and LBW. It provided new insights into the combined effects of EMT and age in FET cycles and offered valuable references for the clinical management and treatment strategies aimed at EMT.

Ovarian stimulation protocols: impact on oocyte and endometrial quality and function

Ovarian stimulation (OS) truly is an art. There exists a myriad of protocols used to achieve the same goal: stimulating the ovaries to produce more than one mature oocyte to improve the chance of a live birth. However, considerable debate remains as to whether OS impacts oocyte and endometrial quality to affect in vitro fertilization outcomes. Although "more is better" has long been considered the best approach for oocyte retrieval, this review challenges that notion by examining the influence of stimulation on oocyte quality. Likewise, improved outcomes after frozen blastocyst transfer suggest that OS perturbs endometrial preparation and/or receptivity, although correlating changes with implantation success remains a challenge. Therefore, the focus of this review is to summarize our current understanding of perturbations in human oocyte quality and endometrial function induced by exogenous hormone administration. We highlight the need for further research to identify more appropriate markers of oocyte developmental competence as well as those that define the roles of the endometrium in the success of assisted reproductive technology.

The embryo stage at fresh ET does not affect the cumulative live birth rate in women with a thin endometrium: a retrospective matched-controlled cohort study

Background

The blastocyst-stage embryo has been considered more advantageous for increasing the cumulative live birth rate (CLBR) at fresh embryo transfer (ET) compared to the cleavage-stage embryo. However, it remains uncertain whether this advantage extends to specialized subpopulations, such as women with thin endometrium (TE), who are characteristic of impaired endometrial receptivity. Thus, this study aims to evaluate the difference in the CLBR between cleavage-stage and blastocyst-stage embryos at fresh ET specifically in women with TE.

Methods

A retrospective cohort comprising 1089 women from three centers, ranging from September 2017 to January 2022, was established. These women were diagnosed with TE (defined as endometrium thickness <= 8 mm) and underwent their first fresh ET. To create a comparable cohort between the cleavage and blastocyst groups while adjusting for key covariates, the propensity score matching (PSM) method was employed. The primary outcome assessed was the CLBR per woman. Both cohorts underwent Kaplan-Meier analysis, Cox proportional hazard models, cumulative incidence function (CIF) curve analysis, and Fine-Grey competing risk models to ascertain the impact of embryo stage at fresh ET on CLBR. Additionally, a sensitivity analysis was conducted within a subgroup defining thin endometrium as an endometrium thickness (EMT) < 7 mm.

Results

In the matched cohort after PSM, the CLBR was comparable between groups (p=0.331). However, the cleavage-stage fresh ET was associated with an elevated risk of low birth weight (LBW) (p=0.005) and small for gestational age (SGA) (p=0.037). Kaplan-Meier analysis showed that the median number of embryo transfer cycles was 2 in the cleavage group and 3 in the blastocyst group. The CLBR for the cleavage group reached 78.1%, while the blastocyst group reached 60.0% after 5 cycles of embryo transfers (log-rank test, p=0.09). A multivariable Cox proportional hazard model indicated no significant association between the embryo stage at fresh ET and CLBR (HR=0.80, 95% CI=0.60-1.07). The CIF curve and Fine-Grey competing risk models demonstrated similar results. These analyses were repeated in the original cohort before PSM and in the subgroup with EMT < 7 mm, and the results remained robust.

Conclusion

For TE women receiving fresh ET, the choice between the cleavage-stage embryo and the blastocyst-stage embryo yields comparable CLBR. However, selecting the cleavage-stage embryo is associated with increased risks of LBW and SGA births.

Relationship between fresh single embryo morphology scores and serum HCG values at 14 days and 14-18-day doubling values

RESEARCH QUESTION

What is the effect of embryo morphology score on 14-day β-HCG levels and 14-18-day β-HCG doubling values, and do they have differences in day-3 embryo or day-5 blastocyst transfers?

DESIGN

Retrospective analysis of 4434 fresh cycles of single embryo transfers (SET) with β-HCG ≥15 mIU/ml on day 14 after transfer via IVF and ICSI. The correlation between embryo morphology score and 14-day β-HCG was examined. Doubling of 14-18 day β-HCG was analysed in 2628 cycles to determine correlations with embryo morphology score.

RESULTS

In day-3 SET, number of embryonic cells was positively correlated with 14-day post-transfer β-HCG values (R = 0.076; P = 0.013). No significant correlation was observed between the grade of the transferred embryos and the 14-18-day serum β-HCG doubling values. In day-5 single blastocyst transfers, the degree of blastocyst expansion, trophoblast cell and inner cell mass (ICM) grades demonstrated a significant positive correlation with 14-day post-transfer β-HCG (P < 0.001, P = 0.014, P = 0.003). Degree of blastocyst expansion was significantly correlated with 14-18-day β-HCG doubling values (R = -0.051, P = 0.027). Grades of the ICM and trophoblast cells showed no significant correlation with 14-18-day β-HCG doubling values.

CONCLUSION

In fresh SET, embryo morphology score influences 14-day β-HCG values in day-3 embryos and day-5 blastocyst transfers. Embryo morphology score in day-3 SET does not affect 14-18-day β-HCG doubling values. Degree of blastocyst expansion significantly affects 14-18-day β-HCG doubling values in day-5 blastocyst transfers.

Subendometrial blood flow detected by Doppler ultrasound associates with pregnancy outcomes of frozen embryo transfer in patients with thin endometrium

PURPOSE

Multiple factors have been shown to influence the rate of clinical pregnancy after FET in IVF treatment, including embryo quality, synchronization of embryo and endometrium, and endometrial receptivity (ER). The subendometrial blood flow conditions could also contribute potentially major effects toward the establishment and maintenance of pregnancy. We conducted a retrospective cohort study to examine the correlation between subendometrial blood flow, as determined by Doppler ultrasound, and pregnancy outcomes in IVF patients with a thin endometrium (endometrium thickness [EMT] ≤ 0.7 cm).

METHODS

This was a retrospective cohort study conducted at a university-affiliated reproductive hospital from January 2017 to April 2023. The EMT and subendometrial blood flows were assessed using transvaginal color Doppler ultrasound and evaluated by experienced clinical ultrasound physicians on the endometrial transformation day. The pregnancy outcomes were followed up and documented in clinical medical records through the IVF cohort study at our center.

RESULTS

In the patients with 0.5 cm ≤ EMT ≤ 0.7 cm, the embryo implantation rate was statistically significant increased in the patients with the presence of subendometrial blood flow (OR 1.484; 95% CI, 1.001-2.200; P = 0.049; aOR 1.425; 95% CI, 1.030-2.123; P = 0.003). Patients with discernible subendometrial blood flow have superior live birth (P = 0.028), clinical pregnancy (P = 0.049), and embryo implantation (P = 0.027) compared to the patients without subendometrial blood flow when the EMT is ≤ 0.7 cm.

CONCLUSIONS

The presence of subendometrial blood flow detected by ultrasound was positively associated with successful embryo implantation and favorable pregnancy outcomes in patients with thin endometrium undergoing FET.

Impact of elevated serum estradiol levels before progesterone administration on pregnancy outcomes in frozen-thawed embryo transfer for hormone replacement therapy

OBJECTIVE

The objective of this retrospective cohort study is to investigate the impact of monitoring serum estradiol (E2) levels before progesterone administration within hormone replacement therapy (HRT) on pregnancy outcomes in women undergoing frozen-thawed embryo transfer (FET).

METHODS

Analyzed HRT-FET cycles conducted at a reproductive center from 2017 to 2022. Serum E2 levels were measured prior to progesterone administration. Multivariate stratified and logistic regression analyses were performed on 26,194 patients grouped according to terciles of serum E2 levels before progesterone administration.

RESULTS

The clinical pregnancy rate (CPR) and live birth rate (LBR) exhibited a gradual decline with increasing serum E2 levels across the three E2 groups. Even after controlling for potential confounders, including female age, body mass index, infertility diagnosis, cycle category, number of embryos transferred, fertilization method, indication for infertility, and endometrial thickness, both CPR and LBR persistently showed a gradual decrease as serum E2 levels increased within the three E2 groups. The same results were obtained by multivariate logistic regression analysis.

CONCLUSIONS

This large retrospective study indicates that elevated serum E2 levels before progesterone administration during HRT-FET cycles are associated with reduced CPR and LBR post-embryo transfer. Therefore, it is advisable to monitor serum E2 levels and adjust treatment strategies accordingly to maximize patient outcomes.

Walking on thin endometrium

PURPOSE OF REVIEW

Endometrial thickness has been regarded a predictor of success in assisted reproductive technology cycles and it seems a common practice to cancel embryo transfer when it is below a cut-off. However, various cut-offs have been proposed without a causal relationship between endometrial thickness and embryo implantation being established, casting doubt on the current dogma.

RECENT FINDINGS

Methodological limitations of the available studies on endometrial thickness are increasingly recognized and better designed studies do not demonstrate a cut-off value which requires cancelling an embryo transfer.

SUMMARY

Endometrium is important for implantation and a healthy pregnancy; however, ultrasound measured thickness does not seem to be a good marker of endometrial function.