The Metabolomic Profile of Spent Culture Media from Day-3 Human Embryos Cultured under Low Oxygen Tension

Blastulation time measured with time-lapse system can predict in vitro viability of bovine blastocysts

The objective of this study was to evaluate the time of blastulation monitored by time-lapse technology to predict in vitro viability of bovine blastocysts. This technology can be a powerful tool for bovine embryos selection with higher implantation capacity and competence. Also, in humans an early blastulation is associated with higher quality and pregnancy rate. Cumulus oocyte complexes (COCs) were matured for 20 to 22 h and then fertilized by co-incubation of COCs and spermatozoa (10,000 sperm per oocyte) for 18 h. Presumptive zygotes were placed individually in microwells, in droplets of commercial culture medium. The Primo Vision TL system (EVO+; Vitrolife) captured digital images of developing embryos every 15 minutes. The time frame from IVF to the start of blastulation (tSB) and to blastocyst development (tB) was recorded. After day 7.5, the blastocysts were in vitro culture for 48 h until day 9.5 after IVF to evaluate post hatching development. In vitro viability was evaluated at day 9.5: those with a diameter greater than 200 μm and a total cell count greater than 180 were classified as viable (value 1), while the rest were classified as non in vitro viable (value 0). The area under the ROC curve (AUC) was estimated to determine the predictive power of in vitro viability through blastulation time. In addition, binary logistic regression analysis was used to generate a mathematical model with morphokinetic variables that allow the best prediction of in vitro viability. In 13 sessions, the blastocyst production rate was 46.2% (96/208). The cut-off time to discriminate early or late blastulation was 149.8 h. The post-hatching development of the embryos with early blastulation was 63.3% (31/49), being statistically superior (p = 0.001) than the late blastulation group 14.9% (7/47). Likewise, the time of blastulation showed an accuracy of 90.8% (p < 0.001) in predicting in vitro viability of bovine blastocysts. In conclusion, the selection of blastocysts based on blastulation time (< 155 h) and blastocyst diameter measured on day 7.5 after IVF (> 180 μm) maximizes the in vitro viability.

Unraveling the Consequences of Oxygen Imbalance on Early Embryo Development: Exploring Mitigation Strategies

Although well-established and adopted by commercial laboratories, the in vitro embryo production system still requires refinements to achieve its highest efficiency. Early embryonic development is a dynamic event, demanding suitable conditions to provide a high number of embryos with quality and competence. The first step to obtaining an optimized in vitro environment is to know the embryonic metabolism and energy request throughout the different stages of development. Oxygen plays a crucial role in several key biological processes necessary to sustain and complete embryonic development. Nonetheless, there is still controversy regarding the optimal in vitro atmospheric concentrations during culture. Herein, we discuss the impact of oxygen tension on the viability of in vitro-produced embryos during early development. The importance of oxygen tension is addressed as its roles regarding essential embryonic traits, including embryo production rates, embryonic cell viability, gene expression profile, epigenetic regulation, and post-cryopreservation survival. Finally, we highlight the damage caused by in vitro unbalanced oxygen tensions and strategies to mitigate the harmful effects.

Metabolic signature of spent culture media shows lipid metabolism as a determinant of pregnancy outcomes

In the present study, we investigated the spent culture media of in vitro produced (IVP) bovine embryos which did (group Pregnant) or did not (group Non-pregnant) establish pregnancy after transfer. For that purpose, IVP embryos on D5 were transferred to individual droplets for the last 48 h of culture. Embryos at the blastocyst stage were then transferred to synchronized recipients, while respective culture media drops were collected and evaluated individually. The list of metabolites present in spent culture media was obtained by electrospray ionization mass spectrometry (ESI-MS) and analysed with Metaboanalyst® to characterize the metabolic profile of each group. The spectrometric analysis showed that pathways related to lipid metabolism, particularly fatty acids degradation via beta-oxidation, were more present in the Pregnant group whereas no significant pathway was identified in the group Non-pregnant. By using this method, we were able to identify a metabolic signature in culture media that allows for a better comprehension of preferential metabolic routes taken by the most viable embryos. These findings offer great insights into the biochemistry of embryo development and reveal a potential target for the development of better-quality IVP systems, as well as tools to identify bovine embryos with greater chances to establish and maintain pregnancy.

Effects of changing culture medium on preimplantation embryo development in rabbit

Many studies have focused on the optimization of the composition of embryo culture medium; however, there are few studies involving the effect of a culture medium changing procedure on the preimplantation development of embryos. In this study, three groups were designed: a non-renewal group, a renewal group and a half-renewal group. The levels of reactive oxygen species (ROS), apoptotic index, blastocyst ratio and blastocyst total cell number were analyzed in each group. The results showed that the ROS level and the apoptotic index of blastocyst in the non-renewal group were significantly higher than in the renewal group and the half-renewal group (P < 0.05). The blastocyst ratio and blastocyst total cell number were significantly higher in the half-renewal group than that in non-renewal group and the renewal group (P < 0.05). These results demonstrated that the procedure of changing the culture medium influenced ROS level, apoptotic index, blastocyst ratio and total cell number of blastocysts. In addition, the result suggested that changing the culture medium may lead to a loss of important regulatory factors for embryos, while not changing the culture medium may lead to the accumulation of toxic substances. Half-renewal can alleviate the defects of both no renewal and renewal, and benefit embryo development. This study will be of high value as a reference for the optimization of embryo culture in vitro, and is very significant for assisted reproduction.

The influence of oxygen concentration during embryo culture on obstetric and neonatal outcomes: a secondary analysis of a randomized controlled trial

STUDY QUESTION

Does oxygen concentration during 3-day embryo culture affect obstetric and neonatal outcomes?

SUMMARY ANSWER

Oxygen concentration during 3-day embryo culture does not seem to affect the obstetric and neonatal outcomes measured.

WHAT IS KNOWN ALREADY

Atmospheric oxygen appears to be harmful during extended embryo culture. Embryo culture conditions might therefore be a potential risk factor for subsequent fetal development and the health of future children. No data are available concerning the obstetrics and neonatal outcomes after Day 3 transfer of embryos cultured under reduced and atmospheric oxygen tensions.

STUDY DESIGN, SIZE, DURATION

A secondary analysis of a previous randomized controlled trial assessing clinical pregnancy outcomes was carried out. This analysis included 1125 consecutive oocyte donation cycles utilizing ICSI or IVF and Day 3 embryo transfers between November 2009 and April 2012. The whole cohort of donated oocytes from patients who agreed to participate in the study were randomly allocated (1:1 ratio) to a reduced O2 tension group (6% O2) or an air-exposed group (20% O2) based on a computer-generated randomization list. Fresh and vitrified oocytes were used for oocyte donation. Only those pregnancies with a live birth at or beyond 24 weeks of gestation were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Day 3 embryos were cultured in an atmosphere of 5.5% CO2, 6% O2, 88.5% N2 versus a dual gas system in air.

MAIN RESULTS AND THE ROLE OF CHANCE

From the eligible 1125 cycles, 564 were allocated to the 6% O2 group and 561 cycles to the 20% O2 group. However, 50 and 62 cycles did not reach embryo transfer in the 6% and 20% O2 groups, respectively. No differences were found between 6% O2 and atmospheric O2 tension in the number of livebirths per embryo transfer (mean ± SD, 0.5 ± 0.7 versus 0.5 ± 0.7), pregnancy complications or neonatal outcomes. Both groups (6% and atmospheric O2) had similar single and twin delivery rates (40.8% versus 38.1% and 10.7% versus 12.3%, respectively). Preterm delivery rates and very preterm delivery rates (10.80% versus 13.24% and 1.25% versus 2.94%, respectively), birthweight (3229 ± 561 g versus 3154 ± 731 g), low birthweight (2.92% versus 2.45%), birth height (50.18 ± 2.41 cm versus 49.7 ± 3.59 cm), head circumference (34.16 ± 1.87 cm versus 33.09 ± 1.85 cm) and 1 min Apgar scores (8.96 ± 0.87 versus 8.89 ± 0.96) were also similar between 6% and atmospheric O2 groups, respectively.

LIMITATIONS, REASONS FOR CAUTION

The number of liveborns finally analyzed is still small and not all obstetric and neonatal variables could be evaluated. Furthermore, a small proportion of the obstetric and neonatal data was obtained through a questionnaire filled out by the patients themselves. One reason for the lack of effect of oxygen concentration on pregnancy outcome could be the absence of trophectoderm cells at cleavage stage, which may make Day 3 embryos less susceptible to hypoxic conditions.

WIDER IMPLICATIONS OF THE FINDINGS

Nowadays many IVF laboratories use a more physiological oxygen concentration for embryo culture. However, the benefits of using low oxygen concentration on both laboratory and clinical outcomes during embryo culture are still under debate. Furthermore, long-term studies investigating the effect of using atmospheric O2 are also needed. Gathering these type of clinical data is indeed, quite relevant from the safety perspective. The present data show that, at least in egg donation cycles undergoing Day 3 embryo transfers, culturing embryos under atmospheric oxygen concentration seems not to affect perinatal outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

The present project was supported by the R + D program of the Regional Valencian Government, Spain (IMPIVA IMDTF/2011/214). The authors declare that they have no conflict of interest with respect to the content of this manuscript.

TRIAL REGISTRATION NUMBER

NCT01532193.

Endometrial injection of embryo culture supernatant for subfertile women in assisted reproduction

BACKGROUND

Despite substantial improvements in the success of assisted reproduction techniques (ART), live birth rates may remain consistently low, and practitioners may look for innovative treatments to improve the outcomes. The injection of embryo culture supernatant in the endometrial cavity can be undertaken at various time intervals before embryo transfer. It provides an altered endometrial environment through the secretion of factors considered to facilitate implantation. It is proposed that injection of the supernatant into the endometrial cavity prior to embryo transfer will stimulate the endometrium and provide better conditions for implantation to take place. An increased implantation rate would subsequently increase rates of clinical pregnancy and live birth, but current robust evidence on the efficacy of injected embryo culture supernatant is lacking.

OBJECTIVES

To evaluate the effectiveness and safety of endometrial injection of embryo culture supernatant before embryo transfer in women undergoing ART.

SEARCH METHODS

Our search strategies were designed with the help of the Cochrane Gynaecology and Fertility Group Information Specialist. We sought to identify all published and unpublished randomised controlled trials (RCTs) meeting inclusion criteria. Searches were performed on 2 December 2019. We searched the Cochrane Gynaecology and Fertility Group Specialised Register of controlled trials, CENTRAL, MEDLINE, Embase, CINAHL, trials registries and grey literature. We made further searches in the UK National Institute for Health and Care Excellence (NICE) fertility assessment and treatment guidelines. We handsearched reference lists of relevant systematic reviews and RCTs, together with searches of PubMed and Google for any recent trials that have not yet been indexed in the major databases. We had no language or location restrictions.

SELECTION CRITERIA

We included RCTs testing the use of endometrial injection of embryo culture supernatant before embryo transfer during an ART cycle, compared with the non-use of this intervention, the use of placebo or the use of any other similar drug.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed risk of bias, extracted data from studies and attempted to contact the authors where data were missing. We pooled studies using a fixed-effect model. Our primary outcomes were live birth/ongoing pregnancy and miscarriage. We performed statistical analysis using Review Manager 5. We assessed evidence quality using GRADE methods.

MAIN RESULTS

We found five RCTs suitable for inclusion in the review (526 women analysed). We made two comparisons: embryo culture supernatant use versus standard care or no intervention; and embryo culture supernatant use versus culture medium. All studies were published as full-text articles. Data derived from the reports or through direct communication with investigators were available for the final meta-analysis performed. The GRADE evidence quality of studies ranged from very low-quality to moderate-quality. Factors reducing evidence quality included high risk of bias due to lack of blinding, unclear risk of publication bias and selective outcome reporting, serious inconsistency among study outcomes, and serious imprecision due to wide confidence intervals (CIs) and low numbers of events. Comparison 1. Endometrial injection of embryo culture supernatant before embryo transfer versus standard care or no intervention: One study reported live birth only and two reported the composite outcome live birth and ongoing pregnancy. We are uncertain whether endometrial injection of embryo culture supernatant before embryo transfer during an ART cycle improves live birth/ongoing pregnancy rates compared to no intervention (odds ratio (OR) 1.11, 95% CI 0.73 to 1.70; 3 RCTs; n = 340, I² = 84%; very low-quality evidence). Results suggest that if the chance of live birth/ongoing pregnancy following placebo or no treatment is assumed to be 42%, the chance following the endometrial injection of embryo culture supernatant before embryo transfer would vary between 22% and 81%. We are also uncertain whether the endometrial injection of embryo culture supernatant could decrease miscarriage rates, compared to no intervention (OR 0.89, 95% CI 0.44 to 1.78, 4 RCTs, n = 430, I² = 58%, very low-quality evidence). Results suggest that if the chance of miscarriage following placebo or no treatment is assumed to be 9%, the chance following injection of embryo culture supernatant would vary between 3% and 30%. Concerning the secondary outcomes, we are uncertain whether the injection of embryo culture supernatant prior to embryo transfer could increase clinical pregnancy rates (OR 1.13, 95% CI 0.80 to 1.61; 5 RCTs; n = 526, I² = 0%; very low-quality evidence), decrease ectopic pregnancy rates (OR 0.32, 95% CI 0.01 to 8.24; n = 250; 2 RCTs; I² = 41%; very low-quality evidence), decrease multiple pregnancy rates (OR 0.70, 95% CI 0.26 to 1.83; 2 RCTs; n = 150; I² = 63%; very low-quality evidence), or decrease preterm delivery rates (OR 0.63, 95% CI 0.17 to 2.42; 1 RCT; n = 90; I² = 0%; very low-quality evidence), compared to no intervention. Finally, there may have been little or no difference in foetal abnormality rates between the two groups (OR 3.10, 95% CI 0.12 to 79.23; 1 RCT; n = 60; I² = 0%; low-quality evidence). Comparison 2. Endometrial injection of embryo culture supernatant versus endometrial injection of culture medium before embryo transfer We are uncertain whether the use of embryo culture supernatant improves clinical pregnancy rates, compared to the use of culture medium (OR 1.09, 95% CI 0.48 to 2.46; n = 96; 1 RCT; very low-quality evidence). No study reported live birth/ongoing pregnancy, miscarriage, ectopic or multiple pregnancy, preterm delivery or foetal abnormalities.

AUTHORS' CONCLUSIONS

We are uncertain whether the addition of endometrial injection of embryo culture supernatant before embryo transfer as a routine method for the treatment of women undergoing ART can improve pregnancy outcomes. This conclusion is based on current available data from five RCTs, with evidence quality ranging from very low to moderate across studies. Further large well-designed RCTs reporting on live births and adverse clinical outcomes are still required to clarify the exact role of endometrial injection of embryo culture supernatant before embryo transfer.

New markers of human cumulus oophorus cells cultured in vitro – transcriptomic profile

The presence of CCs around the oocyte after ovulation is one of the key elements contributing to oocyte developmental competence. In the presented study, we used CCs from 12 patients aged 18-40 diagnosed with infertility. After harvesting cells on day 1, 7, 15 and 30 of culture, total RNA was isolated and transcriptomic analysis was performed. The DAVID software indicated the following GO BP terms: “cell junction organization”, “cell migration”, “cell morphogenesis involved in differentiation”, “cell morphogenesis” and “cell motility”. Of the genes belonging to all ontological groups, the most downregulated were: SLC7A8, DFNB31, COL1A1, CDC42SE1, TGFBR3, HMGB1, with the most upregulated genes being: ANXA3, KIAA1199, HTR2B, VCAM1, DKK1.

While many studies focus on attempts to obtain fully competent oocytes, scientists still have difficulty attaining adequate results in vitro. Lack of adequate knowledge often results in low in vitro fertilization efficiency. Therefore, our research focuses on CCs cells, thanks to which the oocyte most likely acquires developmental competence. The main purpose of the study was to identify the potential molecular markers responsible for cell junction organization, migration, differentiation, morphogenesis and motility.

Running title: New markers of human cumulus oophorus cells cultured in vitro

Metabolomics for improving pregnancy outcomes in women undergoing assisted reproductive technologies

BACKGROUND

In order to overcome the low effectiveness of assisted reproductive technologies (ART) and the high incidence of multiple births, metabolomics is proposed as a non-invasive method to assess oocyte quality, embryo viability, and endometrial receptivity, and facilitate a targeted subfertility treatment.

OBJECTIVES

To evaluate the effectiveness and safety of metabolomic assessment of oocyte quality, embryo viability, and endometrial receptivity for improving live birth or ongoing pregnancy rates in women undergoing ART, compared to conventional methods of assessment.

SEARCH METHODS

We searched the Cochrane Gynaecology and Fertility Group Trials Register, CENTRAL, MEDLINE, Embase, CINAHL and two trial registers (Feburary 2018). We also examined the reference lists of primary studies and review articles, citation lists of relevant publications, and abstracts of major scientific meetings.

SELECTION CRITERIA

Randomised controlled trials (RCTs) on metabolomic assessment of oocyte quality, embryo viability, and endometrial receptivity in women undergoing ART.

DATA COLLECTION AND ANALYSIS

Pairs of review authors independently assessed trial eligibility and risk of bias, and extracted the data. The primary outcomes were rates of live birth or ongoing pregnancy (composite outcome) and miscarriage. Secondary outcomes were clinical pregnancy, multiple and ectopic pregnancy, cycle cancellation, and foetal abnormalities. We combined data to calculate odds ratios (ORs) for dichotomous data and 95% confidence intervals (CIs). Statistical heterogeneity was assessed using the I² statistic. We assessed the overall quality of the evidence for the main comparisons using GRADE methods.

MAIN RESULTS

We included four trials with a total of 924 women, with a mean age of 33 years. All assessed the role of metabolomic investigation of embryo viability. We found no RCTs that addressed the metabolomic assessment of oocyte quality or endometrial receptivity.We found low-quality evidence of little or no difference between metabolomic and non-metabolomic assessment of embryos for rates of live birth or ongoing pregnancy (OR 1.02, 95% CI 0.77 to 1.35, I² = 0%; four RCTs; N = 924), live birth alone (OR 0.99, 95% CI 0.69 to 1.44, I² = 0%; three RCTs; N = 597), or miscarriage (OR 1.18, 95% CI 0.77 to 1.82; I² = 0%; three RCTs; N = 869). A sensitivity analysis excluding studies at high risk of bias did not change the interpretation of the results for live birth or ongoing pregnancy (OR 0.90, 95% CI 0.66 to 1.25, I² = 0%; two RCTs; N = 744). Our findings suggested that if the rate of live birth or ongoing pregnancy was 36% in the non-metabolomic group, it would be between 32% and 45% with the use of metabolomics.We found low-quality evidence of little or no difference between groups in rates of clinical pregnancy (OR 1.11, 95% CI 0.85 to 1.45; I²= 44%; four trials; N = 924) or multiple pregnancy (OR 1.50, 95% CI 0.70 to 3.19; I² = 0%; two RCTs, N = 180). Rates of cycle cancellation were higher in the metabolomics group (OR 1.78, 95% CI 1.18 to 2.69; I² = 51%; two RCTs; N = 744, low quality evidence). There was very low-quality evidence of little or no difference between groups in rates of ectopic pregnancy rates (OR 3.00, 95% CI 0.12 to 74.07; one RCT; N = 417), and foetal abnormality (no events; one RCT; N = 125). Data were lacking on other adverse effects. A sensitivity analysis excluding studies at high risk of bias did not change the interpretation of the results for clinical pregnancy (OR 1.03, 95% CI 0.76 to 1.38; I² = 40%; two RCTs; N = 744).The overall quality of the evidence ranged from very low to low. Limitations included serious risk of bias (associated with poor reporting of methods, attrition bias, selective reporting, and other biases), imprecision, and inconsistency across trials.

AUTHORS' CONCLUSIONS

According to current trials in women undergoing ART, there is no evidence to show that metabolomic assessment of embryos before implantation has any meaningful effect on rates of live birth, ongoing pregnancy, miscarriage, multiple pregnancy, ectopic pregnancy or foetal abnormalities. The existing evidence varied from very low to low-quality. Data on other adverse events were sparse, so we could not reach conclusions on these. At the moment, there is no evidence to support or refute the use of this technique for subfertile women undergoing ART. Robust evidence is needed from further RCTs, which study the effects on live birth and miscarriage rates for the metabolomic assessment of embryo viability. Well designed and executed trials are also needed to study the effects on oocyte quality and endometrial receptivity, since none are currently available.

Metabolomics for improving pregnancy outcomes in women undergoing assisted reproductive technologies

BACKGROUND

In order to overcome the low effectiveness of assisted reproductive technologies (ART) and the high incidence of multiple births, metabolomics is proposed as a non-invasive method to assess oocyte quality, embryo viability, and endometrial receptivity, and facilitate a targeted subfertility treatment.

OBJECTIVES

To evaluate the effectiveness and safety of metabolomic assessment of oocyte quality, embryo viability, and endometrial receptivity for improving live birth or ongoing pregnancy rates in women undergoing ART, compared to conventional methods of assessment.

SEARCH METHODS

We searched the Cochrane Gynaecology and Fertility Group Trials Register, CENTRAL, MEDLINE, Embase, CINAHL and two trial registers (November 2016). We also examined the reference lists of primary studies and review articles, citation lists of relevant publications, and abstracts of major scientific meetings.

SELECTION CRITERIA

Randomised controlled trials (RCTs) on metabolomic assessment of oocyte quality, embryo viability, and endometrial receptivity in women undergoing ART.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and risk of bias, and extracted the data. The primary outcomes were rates of live birth or ongoing pregnancy (composite outcome) and miscarriage. Secondary outcomes were clinical pregnancy, multiple and ectopic pregnancy, cycle cancellation, and foetal abnormalities. We combined data to calculate odds ratios (ORs) for dichotomous data and 95% confidence intervals (CIs). Statistical heterogeneity was assessed using the I² statistic. We assessed the overall quality of the evidence for the main comparisons using GRADE methods.

MAIN RESULTS

We included four trials with a total of 802 women, with a mean age of 33 years. All assessed the role of metabolomic investigation of embryo viability. We found no RCTs that addressed the metabolomic assessment of oocyte quality or endometrial receptivity.We found low-quality evidence of little or no difference between metabolomic and non-metabolomic assessment of embryos for rates of live birth or ongoing pregnancy (OR 1.11, 95% CI 0.83 to 1.48; I² = 0%; four RCTs; N = 802), or miscarriage (OR 0.96, 95% CI 0.52 to 1.78; I² = 0%; two RCTs; N = 434). A sensitivity analysis excluding studies at high risk of bias did not change the interpretation of the results for live birth or ongoing pregnancy (OR 0.99, 95% CI 0.71 to 1.38; I² = 0%; two RCTs; N = 621). Our findings suggested that if the rate of live birth or ongoing pregnancy was 36% in the non-metabolomic group, it would be between 32% and 45% with the use of metabolomics.We found low-quality evidence of little or no difference between groups in rates of clinical pregnancy (OR 1.22, 95% CI 0.92 to 1.62; I²= 26%; four trials; N = 802), or multiple pregnancy (OR 1.52, 95% CI 0.71 to 3.23; I² = 0%; two RCTs, N = 181). There was very low-quality evidence of little or no difference between groups in ectopic pregnancy rates (OR 3.37, 95% CI 0.14 to 83.40; one RCT; N = 309), and foetal abnormalities (no events; one RCT; N = 125), and very low-quality evidence of higher rates of cycle cancellation in the metabolomics group (OR 1.78, 95% CI 1.18 to 2.69; I² = 51%; two RCTs; N = 744). Data were lacking on other adverse effects. A sensitivity analysis excluding studies at high risk of bias did not change the interpretation of the results for clinical pregnancy (OR 1.14, 95% CI 0.83 to 1.57; I² = 0%; two RCTs; N = 621).The overall quality of the evidence ranged from very low to low. Limitations included serious risk of bias (associated with poor reporting of methods, attrition bias, selective reporting, and other biases), imprecision, and inconsistency across trials.

AUTHORS' CONCLUSIONS

According to current trials in women undergoing ART, there is insufficient evidence to show that metabolomic assessment of embryos before implantation has any meaningful effect on rates of live birth, ongoing pregnancy, or miscarriage rates. The existing evidence varied from very low to low-quality. Data on adverse events were sparse, so we could not reach conclusions on these. At the moment, there is no evidence to support or refute the use of this technique for subfertile women undergoing ART. Robust evidence is needed from further RCTs, which study the effects on live birth and miscarriage rates for the metabolomic assessment of embryo viability. Well designed and executed trials are also needed to study the effects on oocyte quality and endometrial receptivity, since none are currently available.