A predictive model for high-quality blastocyst based on blastomere number, fragmentation, and symmetry

The Istanbul Consensus update: a revised ESHRE/ALPHA consensus on oocyte and embryo static and dynamic morphological assessment† ‡

This European Society of Human Reproduction and Embryology (ESHRE)/Alpha Scientists in Reproductive Medicine (ALPHA) consensus document provides several novel recommendations to assess oocyte and embryo morphology and rank embryos for transfer. A previous ALPHA/ESHRE consensus on oocyte and embryo morphological assessment was published in 2011. After more than a decade, and the integration of time-lapse technology into embryo culture and assessment, a thorough review and update was needed. A working group consisting of ALPHA members and ESHRE Special interest group of Embryology members formulated recommendations on oocyte and embryo assessment. The working group included 17 internationally recognized experts with extensive experience in clinical embryology. Seven members represented ALPHA and eight members represented ESHRE, along with two methodological experts from the ESHRE central office. Based on a systematic literature search and discussion of existing evidence, the recommendations of the Istanbul Consensus (2011) were reassessed and, where appropriate, updated based on consensus within the working group. A stakeholder review was organized after the updated draft was finalized. The final version was approved by the working group, the ALPHA Executive Committee and the ESHRE Executive Committee. This updated consensus paper provides 20 recommendations focused on the timeline of preimplantation developmental events and morphological criteria for oocyte, zygote and embryo assessment. Based on the duration of embryo culture, recommendations are given on the frequency and timing of assessments to ensure consistency and effectiveness. Several criteria relevant to oocyte and embryo morphology have not been well studied, leading to either a recommendation against their use for grading or for their use in ranking rather than grading. Future updates may require further revision of these recommendations. This document provides embryologists with advice on best practices when assessing oocyte and embryo quality based on the most recent evidence.

The Istanbul consensus update: a revised ESHRE/ALPHA consensus on oocyte and embryo static and dynamic morphological assessment†,‡

STUDY QUESTION

What are the current recommended criteria for morphological assessment of oocytes, zygotes, and embryos?

SUMMARY ANSWER

The present ESHRE/Alpha Scientists in Reproductive Medicine consensus document provides several novel recommendations to assess oocyte and embryo morphology and rank embryos for transfer.

WHAT IS KNOWN ALREADY

A previous Alpha Scientists in Reproductive Medicine/ESHRE consensus on oocyte and embryo morphological assessment was published in 2011. After more than a decade, and the integration of time-lapse technology into embryo culture and assessment, a thorough review and update was needed.

STUDY DESIGN, SIZE, DURATION

A working group consisting of Alpha Scientists in Reproductive Medicine executive committee members and ESHRE Special interest group of Embryology members formulated recommendations on oocyte and embryo assessment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The working group included 17 internationally recognized experts with extensive experience in clinical embryology. Seven members represented Alpha Scientists in Reproductive Medicine and eight members represented ESHRE, along with to two methodological experts from the ESHRE central office. Based on a systematic literature search and discussion of existing evidence, the recommendations of the Istanbul Consensus (2011) were reassessed and, where appropriate, updated based on consensus within the working group. A stakeholder review was organized after the updated draft was finalized. The final version was approved by the working group, the Alpha executive committee and the ESHRE Executive Committee.

MAIN RESULTS AND THE ROLE OF CHANCE

This updated consensus paper provides 20 recommendations focused on the timeline of preimplantation developmental events and morphological criteria for oocyte, zygote, and embryo assessment. Based on duration of embryo culture, recommendations are given on the frequency and timing of assessments to ensure consistency and effectiveness.

LIMITATIONS, REASONS FOR CAUTION

Several criteria relevant to oocyte and embryo morphology have not been well studied, leading to either a recommendation against their use for grading or for their use in ranking rather than grading. Future updates may require further revision of these recommendations.

WIDER IMPLICATIONS OF THE FINDINGS

This document provides embryologists with advice on best practices when assessing oocyte and embryo quality based on the most recent evidence.

STUDY FUNDING/COMPETING INTEREST(S)

The consensus meeting and writing of the paper were supported by funds from ESHRE and Alpha Scientists in Reproductive Medicine. The working group members did not receive any payment. G.C. declared payments or honoraria for lectures from Gedeon Richter and Cooper Surgical. A.C. declared text book royalties (Mastering Clinical Embryology, published 2024), consulting fees from Cooper Surgical, Gedeon Richter and TMRW Life Sciences, honoraria for lectures from Merck, Ferring, and Gedeon Richter, and participation in the HFEA Scientific Advances Committee; she also disclosed being treasurer and vice-president of Alpha Scientists in Reproductive Medicine, a shareholder in Care Fertility Limited and Fertile Mind Limited, and having stock options in TMRW Life Sciences and U-Ploid Biotechnology Ltd. L.R. declared consulting fees from Organon, payments or honoraria for lectures from Merck, Organon, IBSA, Finox, Geden Richter, Origio, Organon, Ferring, Fundation IVI; she also disclosed being a member of the Advisory Scientific Board of IVIRMA (Paid) and a member of the Advisory Scientific Board of Nterilizer (unpaid). I.S. declared payments or honoraria for lectures from Vitrolife and Cooper Surgical, and stock options from Alife Health. M.A. declared payments or honoraria for lectures from Vitrolife and support for attending meetings from Vitrolife and Cooper Surgical (both unrelated to this manuscript). The other authors have no conflicts of interest to declare.

DISCLAIMER

This Good Practice Recommendations (GPRs) document represents the consensus views of the members of this working group based on the scientific evidence available at the time of the meeting. GPRs should be used for information and educational purposes. They should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care or be exclusive of other methods of care reasonably directed to obtaining the same results. They do not replace the need for application of clinical judgement to each individual presentation, or variations based on locality and facility type.

The transfer of double cleavage embryos developed from two four-cell embryos may not represent an optimal treatment strategy in cycles with a greater number of four-cell embryos on Day 2

OBJECTIVE

This study examined the impact of the number of Day 2 four-cell (D2-4C) embryos on double embryo transfer and blastocyst culture therapy in the first in vitro fertilization (IVF) cycle.

METHODS

A retrospective review was performed on 1039 blastocyst culture cycles to compare outcomes between available and unavailable blastocyst cycles, emphasizing the relationship between the number of D2-4C embryos and blastocyst availability. Furthermore, the correlation between four-cell embryo counts and live births was analyzed in 986 transfer cycles.

RESULTS

The analysis revealed that the number of D2-4C embryos independently influenced the availability of blastocysts (odds ratio [OR] 1.693, 95% confidence interval [CI] 1.306-2.195, P < 0.001). Receiver operating characteristic (ROC) analysis indicated that D2-4C embryos displayed the highest predictive value for available blastocysts, with an area under the curve (AUC) of 0.861 (95% CI 0.826-0.896). The cut-off point was determined to be 4.5, particularly for individuals younger than 25 years, where the AUC reached 0.927. This suggests that the number of D2-4C embryos has significant predictive value for available blastocysts. The live birth rate (LBR) of fresh embryo transfers significantly increased with the number of D2-4C embryos (P = 0.004). LBRs for zero, one, and two four-cell embryos in double cleavage embryo transfer were 20.24%, 34.97%, and 38.08%, respectively (P = 0.005). In the twin group, the percentages for zero, one, and two four-cell embryos were 1.21%, 9.75%, and 89.02%, respectively (P < 0.001). Single blastocyst transfer achieved an LBR comparable to that of two four-cell embryos (34.8% vs 39.0%, P = 0.415), while the twin rate significantly decreased with single blastocyst transfer (25.17% vs 1.40%, P < 0.001).

CONCLUSION

The number of D2-4C embryos exhibits significant predictive value for available blastocysts, particularly among young women. Furthermore, most twins resulted from the transfer of double cleavage embryos derived from two four-cell embryos. Consequently, when the D2-4C count exceeds four in a cycle, blastocyst culture therapy is preferred over double cleavage-stage embryo transfer.

Considerations for future modification of The Association for the Study of Reproductive Biology embryo grading system incorporating time-lapse observations

The Association for the Study of Reproductive Biology (ASEBIR) Interest Group in Embryology (in Spanish 'Grupo de Interés de Embriología') reviewed key morphokinetic parameters to assess the contribution of time-lapse technology (TLT) to the ASEBIR grading system. Embryo grading based on morphological characteristics is the most widely used method in human assisted reproduction laboratories. The introduction and implementation of TLT has provided a large amount of information that can be used as a complementary tool for morphological embryo evaluation and selection. As part of IVF treatments, embryologists grade embryos to decide which embryos to transfer or freeze. At the present, the embryo grading system developed by ASEBIR does not consider dynamic events observed through TLT. Laboratories that are using TLT consider those parameters as complementary data for embryo selection. The aim of this review was to evaluate review time-specific morphological changes during embryo development that are not included in the ASEBIR scoring system, and to consider them as candidates to add to the scoring system.

External validation of a model for selecting day 3 embryos for transfer based upon deep learning and time-lapse imaging

RESEARCH QUESTION

Could objective embryo assessment using iDAScore Version 2.0 perform as well as conventional morphological assessment?

DESIGN

A retrospective cohort study of fresh day 3 embryo transfer cycles was conducted at a large reproductive medicine centre. In total, 7786 embryos from 4328 cycles with known implantation data were cultured in a time-lapse incubator and included in the study. Fetal heartbeat (FHB) rate was analysed retrospectively using iDAScore Version 2.0 and conventional morphological assessment associated with the transferred embryos. The pregnancy-prediction performance of the two assessment methods was compared using area under the curve (AUC) values for predicting FHB.

RESULTS

AUC values were significantly higher for iDAScore compared with morphological assessment for all cycles (0.62 versus 0.60; P = 0.005), single-embryo transfer cycles (0.63 versus 0.60; P = 0.043) and double-embryo transfer cycles (0.61 versus 0.59; P = 0.012). For the age subgroups, AUC values were significantly higher for iDAScore compared with morphological assessment in the <35 years subgroup (0.62 versus 0.60; P = 0.009); however, no significant difference was found in the ≥35 years subgroup. In terms of the number of blastomeres, AUC values were significantly higher for iDAScore compared with morphological assessment for both the <8c subgroup (0.67 versus 0.56; P < 0.001) and the ≥8c subgroup (0.58 versus 0.55; P = 0.012).

CONCLUSIONS

iDAScore Version 2.0 performed as well as, or better than, conventional morphological assessment in fresh day 3 embryo transfer cycles. iDAScore Version 2.0 may therefore constitute a promising tool for selecting embryos with the highest likelihood of implantation.

Are testicular sperms superior to ejaculated sperms in couples with previous ART failure due to high rate of fragmented embryos? A retrospective cohort study

Objective

The aim was to clarify whether using testicular sperm reduces embryo fragmentation and improves cycle outcomes.

Methods

Fragmented embryo was defined as an embryo in which fragments account for more than one third of the embryonic surface area. High rate of fragmented embryos was defined by a proportion of fragmented embryos higher than 50%. We recruited infertile couples who had undergone at least one ovarian stimulation cycle using ejaculated sperm but failed to conceive due to high rate of fragmented embryos in each previous cycle. After fully informed consent, the couples agreed to obtain testicular sperm by testicular puncture and use testicular sperm for intracytoplasmic sperm injection (ICSI). The normal fertilization rate, transferable embryo rate, fragmented embryo rate and cycle outcomes were compared between ejaculated sperm group (EJA-sperm group) and testicular sperm group (TESTI-sperm group).

Results

Twenty-two couples who agreed to participate in our study underwent 32 ICSI cycles with ejaculated spermatozoa and 23 ICSI cycles with testicular spermatozoa. Embryo transfers were cancelled in 8 ejaculated cycles and 4 testicular cycles because of no transferable embryos. There were no significant differences in age, normal fertilization rate and high-quality embryo rate between ejaculated and testicular groups. The transferable embryo rate and implantation rate in TESTI-sperm group were significantly higher than those in EJA-sperm group (36.9% vs. 22.0%, p < 0.01; 34.2% vs. 0%, p < 0.001). The fragmented embryo rate in TESTI-sperm group was significantly lower than that in EJA-sperm group (61.2% vs. 75.7%, p < 0.05).

Conclusion

Our small retrospective cohort study suggests that using testicular sperm may be a recommended option for couples with previous ART failure because of high rate of fragmented embryos. Large samples, multicenter studies or randomized controlled trial (RCT) are needed to further confirm the superiority of testicular sperm.

Does the cell number of 0PN embryos on day 3 affect pregnancy and neonatal outcomes following single blastocyst transfer?

Background

0PN zygotes have a low cleavage rate, and the clinical outcomes of cleavage-stage embryo transfers are unsatisfactory. Blastocyst culturing is used to screen 0PN embryos, but whether the cell number of 0PN embryos on day 3 affects the clinical outcomes following single blastocyst transfer is unknown and would be helpful in evaluating the clinical value of these embryos.

Methods

This retrospective study compared 46,804 0PN zygotes, 242 0PN frozen-thawed single blastocyst transfers, and 92 corresponding 0PN singletons with 232,441 2PN zygotes, 3563 2PN frozen-thawed single blastocyst transfers, and 1250 2PN singletons from January 2015 to October 2019 at a tertiary-care academic medical centre. The 0PN and 2PN embryos were divided into two groups: the group with < 6 cells on day 3 and that with ≥ 6 cells. Embryo development, subsequent pregnancy and neonatal outcomes were compared between the two groups.

Results

The cleavage and available blastocyst rates of the 0PN zygotes were much lower than those of the 2PN zygotes (25.9% vs. 97.4%, P < 0.001; 13.9% vs. 23.4%, P < 0.001). In the < 6 cells group, the available blastocyst rate of the cleaved 0PN embryos was significantly lower than that of the 2PN embryos (2.5% vs. 12.7%, P < 0.001). However, in the ≥ 6 cells group, the available blastocyst rate of the 0PN cleaved embryos significantly improved, although it was slightly lower than that of the 2PN embryos (33.9% vs. 35.7%, P = 0.014). Importantly, compared to those of the 2PN single blastocyst transfers, the clinical pregnancy rate, live birth rate, Z-score and malformation rate of the 0PN single blastocyst transfers were not significantly different in either the < 6 cells group (30.4% vs. 39.8%, P = 0.362; 30.4% vs. 31.3%, P = 0.932; 0.89 ± 0.90 vs. 0.42 ± 1.02, P = 0.161; 0% vs. 2.6%, P = 1.000) or the ≥ 6 cells group (50.7% vs. 46.6%, P = 0.246; 39.7% vs. 38.3%, P = 0.677; 0.50 ± 1.23 vs. 0.47 ± 1.11, P = 0.861; 2.4% vs. 1.8%, P = 1.000).

Conclusions

The cell number on day 3 of 0PN embryos affected the subsequent formation of blastocysts but did not influence the subsequent pregnancy and neonatal outcomes of 0PN single blastocyst transfers, which may be beneficial to clinicians counselling patients on the clinical value of 0PN embryos.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04492-7.

The function of the m6A methyltransferase METTL3 in goat early embryo development under hypoxic and normoxic conditions

It has been reported that N6-methyladenosine (m6A) methyltransferase-like 3 (METTL3) plays an important role in zygote genome activation during embryonic development, but the effects of METTL3 under oxidative stress in the early development of goat embryos remain largely unknown. In this study, zygotes were monitored at 72 and 168 h after fertilization, and they developed to the 8-cell stage and blastocyst stage under hypoxic conditions and normoxic conditions. Single-cell transcriptome sequencing was performed at the 8-cell stage and the blastocyst stage in the goat embryos, the differentially expressed METTL3 was screened from the sequencing results. We found that microinjection of small interfering RNA (siRNA) against METTL3 caused developmental arrest, both 8-cell rates (37.45 ± 2.21% vs. 47.09 ± 1.38%; P < 0.01) and blastocyst rates of Si-METTL3 (12.17% ± 2.84 vs. 20.83 ± 3.61%; P < 0.01) in Si-METTL3 group were significantly decreased compared with that of control under hypoxic conditions, significant changes were found in the m6A-related genes and the expression levels of critical transcription factors, such as, NANOG, GATA3, CDX2 and SOX17, were decreased. This study revealed the key role of METTL3 in the regulation of embryonic development under oxidative stress, and laid the foundation for further study of the crucial mechanism of oxidative stress during the early embryonic development of goats.

The effect of Day 3 cell number on pregnancy outcomes in vitrified-thawed single blastocyst transfer cycles

STUDY QUESTION

Does cell number on Day 3 have an impact on pregnancy outcomes in vitrified-thawed single blastocyst transfer cycles?

SUMMARY ANSWER

A low Day 3 cell number (≤5 cells) was independently associated with decreased live birth rate (LBR) during single blastocyst transfer cycles in young women.

WHAT IS KNOWN ALREADY

Day 3 cell number is an effective predictor of IVF success rates when transferring cleavage stage embryos. However, the association between Day 3 blastomere number and pregnancy outcomes after blastocyst transfer is still unknown.

STUDY DESIGN, SIZE, DURATION

A retrospective cohort study of 3543 patients who underwent frozen-thawed single blastocyst transfers from January 2013 to June 2018 at a tertiary-care academic medical center.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Patients were grouped into six groups according to the Day 3 cell number: ≤4 cells, 5 cells, 6 cells, 7 cells, 8 cells and >8 cells. The primary outcome measure was LBR. A logistic regression analysis was performed to explore the independent association between Day 3 blastomere number and LBR after adjustment for some potential confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

In women <35 years old, the LBR varied significantly according to Day 3 cell number, with the rate of 31.2%, 34.4%, 41.9%, 45.1%, 48.1% and 48.2% for the ≤4-cell, 5-cell, 6-cell, 7-cell, 8-cell and >8-cell groups, respectively (P < 0.001). This significant difference was also observed in the high- and low-quality blastocyst subgroups of young women. However, for women ≥35 years old, the rate of live birth was similar between groups. Furthermore, after accounting for confounding factors, the LBR was significantly decreased in the ≤4-cell (adjusted odds ratio (aOR): 0.62, 95% CI: 0.48-0.80, P < 0.001) and 5-cell (aOR: 0.73, 95% CI: 0.57-0.92, P = 0.009) groups as compared to the 8-cell group. Likewise, the blastocysts arising from ≤4-cell (aOR: 0.73, 95% CI: 0.57-0.93, P = 0.010) or 5-cell (aOR: 0.77, 95% CI: 0.61-0.97, P = 0.024) embryos were associated with lower clinical pregnancy rate than those from 8-cell embryos. No significant differences were observed in biochemical pregnancy rate and miscarriage rate.

LIMITATIONS, REASONS FOR CAUTION

A limitation of the current study was its retrospective design. Future prospective studies are needed to confirm our findings.

WIDER IMPLICATIONS OF THE FINDINGS

Our observations suggested that a low Day 3 cell number was related to decreased LBR after blastocyst transfer in young women, which provided vital information for clinicians in selecting blastocyst during IVF treatment.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Natural Science Foundation of China (NSFC) (31770989 to Y.W.; 81671520 to Q.C.) and the Shanghai Ninth People's Hospital Foundation of China (JYLJ030 to Y.W.). The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Comparison of Multivariable Logistic Regression and Other Machine Learning Algorithms for Prognostic Prediction Studies in Pregnancy Care: Systematic Review and Meta-Analysis

BACKGROUND

Predictions in pregnancy care are complex because of interactions among multiple factors. Hence, pregnancy outcomes are not easily predicted by a single predictor using only one algorithm or modeling method.

OBJECTIVE

This study aims to review and compare the predictive performances between logistic regression (LR) and other machine learning algorithms for developing or validating a multivariable prognostic prediction model for pregnancy care to inform clinicians' decision making.

METHODS

Research articles from MEDLINE, Scopus, Web of Science, and Google Scholar were reviewed following several guidelines for a prognostic prediction study, including a risk of bias (ROB) assessment. We report the results based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Studies were primarily framed as PICOTS (population, index, comparator, outcomes, timing, and setting): Population: men or women in procreative management, pregnant women, and fetuses or newborns; Index: multivariable prognostic prediction models using non-LR algorithms for risk classification to inform clinicians' decision making; Comparator: the models applying an LR; Outcomes: pregnancy-related outcomes of procreation or pregnancy outcomes for pregnant women and fetuses or newborns; Timing: pre-, inter-, and peripregnancy periods (predictors), at the pregnancy, delivery, and either puerperal or neonatal period (outcome), and either short- or long-term prognoses (time interval); and Setting: primary care or hospital. The results were synthesized by reporting study characteristics and ROBs and by random effects modeling of the difference of the logit area under the receiver operating characteristic curve of each non-LR model compared with the LR model for the same pregnancy outcomes. We also reported between-study heterogeneity by using τ2 and I2.

RESULTS

Of the 2093 records, we included 142 studies for the systematic review and 62 studies for a meta-analysis. Most prediction models used LR (92/142, 64.8%) and artificial neural networks (20/142, 14.1%) among non-LR algorithms. Only 16.9% (24/142) of studies had a low ROB. A total of 2 non-LR algorithms from low ROB studies significantly outperformed LR. The first algorithm was a random forest for preterm delivery (logit AUROC 2.51, 95% CI 1.49-3.53; I2=86%; τ2=0.77) and pre-eclampsia (logit AUROC 1.2, 95% CI 0.72-1.67; I2=75%; τ2=0.09). The second algorithm was gradient boosting for cesarean section (logit AUROC 2.26, 95% CI 1.39-3.13; I2=75%; τ2=0.43) and gestational diabetes (logit AUROC 1.03, 95% CI 0.69-1.37; I2=83%; τ2=0.07).

CONCLUSIONS

Prediction models with the best performances across studies were not necessarily those that used LR but also used random forest and gradient boosting that also performed well. We recommend a reanalysis of existing LR models for several pregnancy outcomes by comparing them with those algorithms that apply standard guidelines.

TRIAL REGISTRATION

PROSPERO (International Prospective Register of Systematic Reviews) CRD42019136106; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=136106.

The impact of a poor quality embryo on the implantation chance of a good quality one when transferred together: A study on double blastocyst transfers

OBJECTIVE

Embryo quality assessment with morphological evaluation remains the first-line method of assessment to select the best embryo for transfer. We aimed to determine if an effect of poor quality embryos on good quality ones exists, whether by a paracrine effect or an adverse endometrial influence, when they are transferred together.

MATERIALS AND METHODS

We included 412 couples, who underwent intracytoplasmic sperm injection (ICSI) cycles in a tertiary IVF center. Single embryo transfer with a good quality embryo and double embryo transfers with a good + poor quality embryo were evaluated. Overall pregnancy (PR) and live birth rates (LBR) were our main outcome measures.

RESULTS

When PR and LBR are compared, there was no statistical significance between single embryo transfer (SET) and double embryo transfer (DET) groups (51.7 % vs 53.7 %, p = 0.620 and 47 % vs 43.1 %, p = 0.117). When the PR and LBRs were compared between SET from poor cohort and DET group, the outcomes were better in DET group (22.1 % vs 53.7 %, p < 0.001 and 22.1 % vs 43.1 %, p < 0.001). The PR and LBRs of SET from good cohort were significantly better than those of DET (64.4 % vs 53.7 %, p < 0.001 and 57.7 % vs 43.1, p < 0.001). When the PR and LBRs of SET from good cohort and SET from poor cohort were compared, better results were obtained in SET from good cohort.

CONCLUSION

The addition of poor quality embryo even is of benefit to the LBR, in the setting of when there is only one good quality blastocyst available for the transfer.

Impact of embryo quality and endometrial thickness on implantation in natural cycle IVF

Purpose

The aim of this study is to assess the effect of the endometrial thickness and embryo quality on the implantation potential in natural cycle IVF (NC-IVF).

Methods

A retrospective single-center study was performed on 552 single embryo transfers after NC-IVF. The ‘quality' of the embryos was evaluated trough the number and regularity of blastomeres, degree of fragmentation, and nuclear content of cells. Endometrial thickness was measured in millimeters with transvaginal ultrasound on the day of hCG application.

Results

Our findings showed a statistically significant difference in successful implantation until a plateau of 10 mm is reached (p = 0.001). Only one pregnancy was achieved where endometrial thickness was less than 7 mm, and this resulted in an early miscarriage. The predictors of favorable implantation were fragmentation (≤ 10%, p < 0.05) and the number of blastomeres (preferably 8-cell, p < 0.01) on day 3. Embryo quality (R = 0.052) and endometrial thickness (R = 0.18) were closely related to pregnancy rate. The overall implantation rate per embryo transfer was 18.8%.

Conclusions

Embryo quality and endometrial thickness have a significant impact on implantation in NC-IVF. Highest implantation potential has an 8-cell embryo with ≤ 10% fragmentation in the third day following oocyte retrieval. Endometrial thickness of at least 7 mm seems to be the optimal edge of successful pregnancy.