Extended embryo culture in human assisted reproduction treatments

Development and validation of a nomogram for predicting ongoing pregnancy in single vitrified-warmed blastocyst embryo transfer cycles

Introduction

The global adoption of the "freeze-all strategy" has led to a continuous increase in utilization of single vitrified-warmed blastocyst embryo transfer (SVBT) owing to its clinical effectiveness. Accurate prediction of clinical pregnancy is crucial from a patient-centered perspective. However, this remains challenging, with inherent limitations due to the absence of precise and user-friendly prediction tools. Thus, this study primarily aimed to develop and assess a nomogram based on quantitative clinical data to optimize the efficacy of personalized prognosis assessment.

Materials and methods

We conducted a retrospective cohort analysis of ongoing pregnancy data from 658 patients with infertility who underwent SVBT at our center between October 17, 2017, and December 18, 2021. Patients were randomly assigned to the training (n=461) or validation (n=197) cohort for nomogram development and testing, respectively. A nomogram was constructed using the results of the multivariable logistic regression (MLR), which included clinical covariates that were assessed for their association with ongoing pregnancy.

Results

The MLR identified eight significant variables that independently predicted ongoing pregnancy outcomes in the study population. These predictors encompassed maternal physiology, including maternal age at oocyte retrieval and serum anti-Müllerian hormone levels; uterine factors, such as adenomyosis; and various embryo assessment parameters, including the number of fertilized embryos, blastocyst morphology, blastulation day, blastocyst re-expansion speed, and presence of embryo string. The area under the receiver operating characteristic curve in our prediction model was 0.675 (95% confidence interval [CI], 0.622-0.729) and 0.656 (95% CI, 0.573-0.739) in the training and validation cohorts, respectively, indicating good discrimination performance in both cohorts.

Conclusions

Our individualized nomogram is a practical and user-friendly tool that can provide accurate and useful SVBT information for patients and clinicians. By offering this model to patients, clinical stakeholders can alleviate uncertainty and confusion about fertility treatment options and enhance patients' confidence in making informed decisions.

Impact of the number of retrieved oocytes on IVF outcomes: oocyte maturation, fertilization, embryo quality and implantation rate

The process of oocyte retrieval represents a key phase during the cycles of in vitro fertilization (IVF). It involves controlled ovarian stimulation to retrieve the highest number of oocytes possible. According to many previous studies, the higher the number of oocytes the higher the chances of obtaining embryos for multiple transfers. In this study, in total, 1987 patients were retrospectively reviewed to investigate the correlations between the number of retrieved oocytes and the subsequent IVF outcomes. Patients were divided into three groups according to the number of retrieved oocytes (Group 1: ≤5 oocytes; Group 2: 6-15 oocytes; Group 3: ≥15 oocytes). The results showed a significant negative correlation between oocyte number and maturation rate as well as fertilization rate. However, a significant positive correlation was found between oocyte number and the blastulation rate. The implantation rate after fresh embryo transfers was higher in group 2 (6-15 oocytes) compared with group 1 (≤5 oocytes). According to our findings, we conclude that oocyte numbers between 6 and 15 oocytes can result in the highest chances of positive IVF outcomes in terms of embryo quality and fresh embryo transfers with lower risks of ovarian hyperstimulation.

Increased blastomere number is associated with higher live birth rate in day 3 embryo transfer

Purpose

To study the relationship between blastomere number and pregnancy outcomes of day 3 embryo transfers.

Methods

This retrospective cohort study included 2237 fresh single day 3 embryo transfer cycles from October 2013 to November 2020. Patients were divided into six groups according to the blastomere number on day 3: ≤ 6-cell (n = 100), 7-cell (n = 207), 8-cell (n = 1522), 9-cell (n = 187), 10-cell (n = 91) and ≥ 11-cell (n = 130). Generalized estimating equation analysis based on multivariate logistic regression model was performed to adjust for potential confounders.

Results

The live birth rate (LBR) was 19.0%, 27.1%, 38.9%, 32.1%, 44.0% and 53.8% for the ≤ 6-cell, 7-cell, 8-cell, 9-cell, 10-cell and ≥ 11-cell groups, respectively (P < 0.001). Specifically, the ≤ 6-cell group was associated with reduced LBR compared with the 8-cell group (aOR 0.50, 95% CI 0.29–0.86; P = 0.013). Conversely, the odds of live birth were significantly increased in patients transferred with 10-cell embryos (aOR 1.62, 95% CI 1.03–2.53; P = 0.035) and ≥ 11-cell embryos (aOR 2.14, 95% CI 1.47–3.11; P < 0.001) when using the 8-cell embryo group as reference. Similar trends were also observed in the rates of positive hCG test and clinical pregnancy, while no significant differences were detected in miscarriage risk.

Conclusion

Increased blastomere number was associated with higher LBR in fresh single day 3 embryo transfer cycles. This finding questions the consensus on the reduced developmental potential of fast-cleaving embryos. Further large prospective studies are warranted for confirmation.

Obstetric and perinatal outcomes of singleton pregnancies after blastocyst-stage embryo transfer compared with those after cleavage-stage embryo transfer: a systematic review and cumulative meta-analysis

BACKGROUND

Extended embryo culture to blastocyst stage is widely used in IVF and is the default strategy in most clinics. The last decade has witnessed a growing interest in obstetric-perinatal outcomes following blastocyst transfer. Recent studies have challenged the conclusions of systematic reviews that associate risks of preterm birth (PTB) and large for gestational age (LGA) babies with blastocyst transfer. A higher proportion of blastocysts is transferred as frozen-thawed embryos, which may also have added implications.

OBJECTIVE AND RATIONALE

The aim of this study was to conduct an updated systematic review of the obstetric-perinatal outcomes in singleton pregnancies following blastocyst-stage transfer compared to cleavage-stage transfer in IVF/ICSI cycles. Where deemed appropriate, data were combined in cumulative meta-analyses.

SEARCH METHODS

Data sources from Medline, EMBASE, CINAHL, Web of Science, the Cochrane Central Register of Clinical Trials and the International Clinical Trials Registry Platform (ICTRP) (1980-2020) were searched using combinations of relevant keywords. Searches had no language restrictions and were limited to human studies. Observational studies and randomized controlled trials comparing obstetric-perinatal outcomes between singleton pregnancies after blastocyst-stage transfer and those after cleavage-stage transfer in IVF/ICSI cycles were sought. Two independent reviewers extracted data in 2 × 2 tables and assessed the methodological quality of the relevant studies using the Critical Appraisal Skills Programme scoring. Cumulative meta-analyses were carried out with independent analysis of pregnancies after fresh and frozen embryo transfers, using the Comprehensive Meta-Analysis software. If provided by included studies, adjusted effect sizes were combined in a sensitivity analysis.

OUTCOMES

A total of 35 studies were included (n = 520 769 singleton pregnancies). Outcome data suggest singleton pregnancies following fresh blastocyst transfer were associated with higher risk of LGA (risk ratio (RR) 1.14; 95% CI 1.05-1.24) and very PTB (RR 1.17; 95% CI 1.08-1.26) compared to fresh cleavage-stage transfer. Singleton pregnancies following frozen blastocyst transfer were associated with higher risks of LGA (RR 1.17; 95% CI 1.08-1.27), PTB (RR 1.13; 95% CI 1.03-1.24) and caesarean section (RR 1.08; 95% CI 1.03-1.13) but lower risks of small for gestational age (RR 0.84, 95% CI 0.74-0.95) and perinatal mortality (RR 0.70; 95% CI 0.58-0.86). Increased risks of LGA and PTB after frozen blastocyst transfer persisted in the sensitivity analysis, which also showed a significantly increased risk of PTB after fresh blastocyst transfer. Cumulative meta-analyses revealed consistency in prevalence and magnitude of risks for a number of years. Data on other perinatal outcomes are still evolving.

WIDER IMPLICATIONS

While the available evidence is predominantly reassuring in the context of blastocyst-stage embryo transfer, observational data suggest that blastocyst transfer is associated with a higher risk of LGA. This holds true irrespective of fresh or frozen transfer. Meta-analysis of adjusted data showed an increased risk of PTB with fresh and frozen blastocyst transfer. However, the quality of available evidence ranges from low to very low. Although blastocyst-stage embryo transfer remains the default position in most centres, based on individual risk profile we may need to consider cleavage-stage embryo transfer in some to mitigate the risk of LGA/PTB.

Should we freeze it? Agreement on fate of borderline blastocysts is poor and does not improve with a modified blastocyst grading system

STUDY QUESTION

What is the inter-observer agreement among embryologists for decision to freeze blastocysts of borderline morphology and can it be improved with a modified grading system?

SUMMARY ANSWER

The inter-observer agreement among embryologists deciding whether to freeze blastocysts of marginal morphology was low and was not improved by a modified grading system.

WHAT IS KNOWN ALREADY

While previous research on inter-observer variability on the decision of which embryo to transfer from a cohort of blastocysts is good, the impact of grading variability regarding decision to freeze borderline blastocysts has not been investigated. Agreement for inner cell mass (ICM) and trophectoderm (TE) grade is only fair, factors which contribute to the grade that influences decision to freeze.

STUDY DESIGN, SIZE, DURATION

This was a prospective study involving 18 embryologists working at four different IVF clinics within a single organisation between January 2019 and July 2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All embryologists currently practicing blastocyst grading at a multi-site organisation were invited to participate. The survey was comprised of blastocyst images in three planes and asked (i) the likelihood of freezing and (ii) whether the blastocyst would be frozen based on visual assessment. Blastocysts varied by quality and were categorised as either top (n = 20), borderline (n = 60) or non-viable/degenerate quality (n = 20). A total of 1800 freeze decisions were assessed. To assess the impact of grading criteria on inter-observer agreement for decision to freeze, the survey was taken once when the embryologists used the Gardner criteria and again 6 months after transitioning to a modified Gardner criterion with four grades for ICM and TE. The fourth grade was introduced with the aim to promote higher levels of agreement for the clinical usability decision when the blastocyst was of marginal quality.

MAIN RESULTS AND THE ROLE OF CHANCE

The inter-observer agreement for decision to freeze was near perfect (kappa 1.0) for top and non-viable/degenerate quality blastocysts, and this was not affected by the blastocysts grading criteria used (top quality; P = 0.330 and non-viable/degenerate quality; P = 0.18). In contrast, the cohort of borderline blastocysts received a mixed freeze rate (average 52.7%) during the first survey, indicative of blastocysts that showed uncertain viability and promoting significant disagreement for decision to freeze among the embryologists (kappa 0.304). After transitioning to a modified Gardner criteria with an additional grading tier, the average freeze rate increased (64.8%; P < 0.0001); however, the inter-observer agreement for decision to freeze was unchanged (kappa 0.301). Therefore, significant disagreement for decision to freeze among embryologists is an ongoing issue not resolved by the two grading criteria assessed here.

LIMITATIONS, REASONS FOR CAUTION

Blastocyst assessment was performed from time-lapse images in three planes, rather than with a microscope in the laboratory. The inter-observer agreement for decision to freeze may be lower for embryologists working in different clinics with different grading protocols.

WIDER IMPLICATIONS OF THE FINDINGS

The decision to freeze a blastocyst with borderline morphology is a common clinical issue that has the potential to arise for any patient during blastocyst culture. Disagreement for decision to freeze these blastocysts, and therefore clinical usability in frozen embryo transfer cycles, affects consistency in patient care due to a potential impact on cumulative live birth rates, as well as financial, emotional and time costs associated with the frozen embryo transfer cycles. We demonstrate significant disagreement for decision to freeze borderline blastocysts among embryologists using the same grading scheme within a large multisite organisation, a phenomenon which was not improved with a modified grading system. Decision-making around borderline embryos is an area requiring further research, especially as studies continue to demonstrate the reduced but modest live birth rates for low quality blastocysts (Grade C). These results provide support for emerging technology for embryo assessment, such as artificial intelligence.

STUDY FUNDING/COMPETING INTEREST(S)

None declared.

TRIAL REGISTRATION NUMBER

Not applicable.

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.

Should we look for a low-grade threshold for blastocyst transfer? A scoping review

Embryo quality is a key determinant of the success of IVF. Although the focus has been on selecting the best embryo for transfer, the classification of low-grade blastocysts (LGB) in existing scoring systems has received less attention. This is worrisome; embryo freezing allows optimal use of all created embryos, thus maximizing the cumulative live birth rate, which is arguably the most important outcome for infertile couples. A PubMed search was conducted in August 2020, using '((('poor-quality' OR 'poor quality') OR ('low-grade' OR 'low grade')) AND ('embryo' OR 'blastocyst')) AND ('pregnancy' OR 'live birth')'. This scoping review shows that LGB have similar euploidy and pregnancy success rates after implantation and have no adverse effects on pregnancy or perinatal outcomes. Evidence for pregnancy outcomes is lacking for different grades of LGB, with most studies clustering all LQB as one to compare with optimal blastocysts.

Do patient factors influence embryologists' decisions to freeze borderline blastocysts?

RESEARCH QUESTION

To investigate whether patient factors influence the decision to freeze a blastocyst with low implantation potential.

DESIGN

This experimental study assessed 170 practicing embryologists from a variety of countries who were recruited via an online survey. Participants were currently practicing embryologists, who grade blastocysts as part of this role. The survey presented decision-making 'vignettes' to participants. These included specific patient information, as well as an image of an expanded blastocyst that was of borderline quality for inner cell mass and trophectoderm, for which the embryologist selected whether or not to freeze. High/low maternal age, the presence/absence of other top quality blastocysts, and the presence/absence of previously unsuccessful IVF cycles were systematically varied within the patient information in a 2 × 2 × 2 design. Participants reported how likely they would be to freeze a particular blastocyst on a scale of 1 (Extremely Unlikely) to 7 (Extremely Likely), and whether or not they would ultimately freeze each blastocyst (Yes or No).

RESULTS

Lower maternal age, no other high-quality blastocysts within the cohort, and multiple unsuccessful IVF cycles were associated with greater likelihood of recommending to freeze (P < .001). Furthermore, significant interactions among all three patient factors were noted.

CONCLUSION

This study provides evidence suggesting that when faced with an uncertain blastocyst, factors pertaining to the patient (maternal age, the presence/absence of other top quality blastocysts, and the presence/absence of previously unsuccessful IVF cycles) influence the decision to freeze.

Deconstructing the myth of poor prognosis for fast-cleaving embryos on day 3. Is it time to change the consensus?

PURPOSE

To determine the developmental competence of fast-cleaving D3 embryos.

METHODS

Retrospective study including 4028 embryos from 513 PGT-A cycles performed between July 2014 and June 2017. Embryos were cultured in time-lapse incubators and biopsied at blastocyst stage. Embryos were classified in groups according to the number of cells on D3 (from 2-cell to ≥13 -cell and compacted). A generalized linear mixed model adjusted for confounding factors was performed to assess the chance to give rise to an euploid blastocyst in each group compared with the chance of 8-cell embryos. Implantation and live birth rates were also analyzed.

RESULTS

The statistical analysis showed that embryos with 9 to 11 cells had a slightly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.77 (0.61-0.96)) while embryos with more than 11 cells were found to be just as likely to give rise to an euploid blastocyst as the 8-cell embryos (OR (95% CI) 1.20 (0.92-1.56)). Conversely, slow-cleaving embryos had a significantly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.31 (0.24-0.39)). Moreover, euploid blastocysts derived from fast-cleaving embryos and from 8-cell embryos exhibit similar live birth rates. No significant differences were found in the chance to give rise a live birth between 8-cell and 9- to 11-cell embryos (OR (95% CI) 1.23 (0.70-2.15)) and > 11-cell embryos (OR (95% CI) 1.09 (0.57-2.09)).

CONCLUSIONS

Embryos with more than 11 cells exhibit similar developmental competence to 8-cell embryos. Their poor prognosis should be reconsidered.

Deconstructing the myth of poor prognosis for fast-cleaving embryos on day 3. Is it time to change the consensus?

PURPOSE

To determine the developmental competence of fast-cleaving D3 embryos.

METHODS

Retrospective study including 4028 embryos from 513 PGT-A cycles performed between July 2014 and June 2017. Embryos were cultured in time-lapse incubators and biopsied at blastocyst stage. Embryos were classified in groups according to the number of cells on D3 (from 2-cell to ≥13 -cell and compacted). A generalized linear mixed model adjusted for confounding factors was performed to assess the chance to give rise to an euploid blastocyst in each group compared with the chance of 8-cell embryos. Implantation and live birth rates were also analyzed.

RESULTS

The statistical analysis showed that embryos with 9 to 11 cells had a slightly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.77 (0.61-0.96)) while embryos with more than 11 cells were found to be just as likely to give rise to an euploid blastocyst as the 8-cell embryos (OR (95% CI) 1.20 (0.92-1.56)). Conversely, slow-cleaving embryos had a significantly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.31 (0.24-0.39)). Moreover, euploid blastocysts derived from fast-cleaving embryos and from 8-cell embryos exhibit similar live birth rates. No significant differences were found in the chance to give rise a live birth between 8-cell and 9- to 11-cell embryos (OR (95% CI) 1.23 (0.70-2.15)) and > 11-cell embryos (OR (95% CI) 1.09 (0.57-2.09)).

CONCLUSIONS

Embryos with more than 11 cells exhibit similar developmental competence to 8-cell embryos. Their poor prognosis should be reconsidered.

Blastocyst culture and transfer in clinically assisted reproduction: a committee opinion

The purposes of this Practice Committee Opinion, which replaces the 2013 ASRM Practice Committee Opinion of the same name (Fertil Steril 2013; 99:667-72), are to review the literature regarding the clinical application of blastocyst transfer and identify the potential risks and laboratory issues related to the use of this technology. This document does not apply to patients undergoing blastocyst culture and transfer for preimplantation genetic testing.

Protein expression in human cumulus cells as an indicator of blastocyst formation and pregnancy success

PURPOSE

The goal for the present study was to implement a technique for protein extraction and identification in human cumulus cells (CCs).

METHODS

Forty samples of CCs were collected after ovum pick-up from patients undergoing intracytoplasmic sperm injection (ICSI). Samples were split into the blastocyst group (n = 10), including patients in which all embryos converted into blastocysts, and the non-blastocyst group (n = 10), including patients in which none of the embryos reached the blastocyst stage or the positive-pregnancy (n = 10) and negative-pregnancy group (n = 10). Proteins were extracted and injected into a liquid chromatography system coupled to a mass spectrometer. The spectra were processed and used to search a database.

RESULTS

There were 87 different proteins in samples from the blastocyst and non-blastocyst groups, in which 30 were exclusively expressed in the blastocyst group and 17 in the non-blastocyst group. Among the 72 proteins detected in the pregnancy groups, 19 were exclusively expressed in the positive, and 16 were exclusively expressed in the negative-pregnancy group.

CONCLUSIONS

CC proteomics may be useful for predicting pregnancy success and the identification of patients that should be included in extended embryo culture programs.

Assessment of human embryo development using morphological criteria in an era of time-lapse, algorithms and 'OMICS': is looking good still important?

With the worldwide move towards single embryo transfer there has been a renewed focus on the requirement for reliable means of assessing embryo viability. In an era of 'OMICS' technologies, and algorithms created through the use of time-lapse microscopy, the actual appearance of the human embryo as it progresses through each successive developmental stage to the blastocyst appears to have been somewhat neglected in recent years. Here we review the key features of the human preimplantation embryo and consider the relationship between morphological characteristics and developmental potential. Further, the impact of the culture environment on morphological traits, how key morphological qualities reflect aspects of embryo physiology, and how computer-assisted analysis of embryo morphology may facilitate a more quantitative approach to selection are discussed. The clinical introduction of time-lapse systems has reopened our eyes and given us a new vantage point from which to view the beauty of the initial stages of human life. Rather than a future in which the morphology of the embryo is deemed irrelevant, we propose that key features, such as multinucleation, cell size and blastocyst differentiation should be included in future iterations of selection/deselection algorithms.

Embryo culture and selection: morphological criteria

In this chapter, we have outlined the various morphological criteria for selection of the best embryo at each important milestone encountered in the progress from the oocyte to the blastocyst. As Gerris et al. stated, a combination of one, two, or even three selection points should lead to a more accurate selection of the best embryo, as no one criterion is better than the other. An embryo that fails to meet the entire set of selection criteria must be avoided as culture cannot correct an impaired embryo.

Pregnancy outcomes of day 5 embryo transfer in patients at high risk of developing ovarian hyperstimulation syndrome and analysis of factors affecting blastocyst formation

OBJECTIVES

To investigate the effects of day 5 embryo transfer (D5ET) compared with day 3 embryo transfer (D3ET) in patients at high risk of developing ovarian hyperstimulation syndrome (OHSS); to analyse factors affecting blastocyst formation.

METHODS

Patients at high risk of developing OHSS underwent either D3ET or D5ET.

RESULTS

A total of 253 patients received D3ET; 263 received D5ET. The number of embryos transferred was lower in the D5ET group than in the D3ET group. There were no between-group differences in pregnancy or live birth rates. Implantation rate was higher, and multifetation rate lower, in the D5ET group compared with the D3ET group. In addition, the incidence of moderate or severe OHSS was lower in the D5ET group than in the D3ET group. The woman's age, gonadotrophin dosage and insemination method were associated with the quality of blastocyst formation.

CONCLUSIONS

In patients with a high risk of developing OHSS, compared with D3ET, D5ET decreased the multifetation rate and the incidence of moderate or severe OHSS, but did not affect the pregnancy or live birth rate. Women of a younger age, who have had an appropriate gonadotrophin dose and insemination by in vitro fertilization, are suitable candidates for blastocyst transfer.

Patient selection criteria for blastocyst transfers in extended embryo culture programs

PURPOSE

To identify the correlation between different cycles, patient factors and blastocyst characteristics.

METHODS

The study included 420 patients undergoing ICSI cycles and 2781 graded blastocysts, which took into account the blastocyst quality. The correlations between the blastocyst parameters and the patient and cycle characteristics were assessed.

RESULTS

The blastocyst development was negatively correlated with the maternal age, BMI and dose of FSH. The ICM was negatively correlated with the FSH dose, whereas the TE quality was influenced by the FSH dose, the maternal age and the number of retrieved oocytes. The embryo morphology on days two and three may predict the blastocyst developmental competence.

CONCLUSIONS

Older patients and patients with high BMI should not be included in extended embryo culture programmes. The extended culture may not favour embryos with poor morphology on days two and three of development. Additionally, a lower ovarian stimulation and decreased oocyte yields may lead to the development of high-quality blastocysts.

Vitrification of in vitro produced bovine embryos: effect of embryonic block and developmental kinetics

In order to investigate whether the kinetics and stage of embryo development affect cryosurvival of in vitro produced bovine embryos, cleaved embryos were categorized in six groups based on their developmental kinetics regarding the stage of embryonic block in bovine (8-16 cell stage): I and II--early (day 2) and late (day 3) 5-8 cell, III and IV--early (day 3) and late (day 4) 8-16 cell, and V and VI--early (day 4) and late (day 5) morula. The cryosurvival and developmental competence of these embryos were compared with each other and also with the corresponding control groups. The potential of 5-8 cell stage embryos to survive vitrification and further develop towards blastocyst stage was significantly lower than vitrified and un-vitrified 8-16 cell and morula stage embryos. These results suggest that, the survival rate and potential of embryos to develop towards blastocyst stage might be affected by the kinetic of the embryo development. Moreover, the results of this study indicated that the optimal stages of early embryo vitrification are post-embryonic block.

Comparing thaw survival, implantation and live birth rates from cryopreserved zygotes, embryos and blastocysts

CONTEXT:

Most in vitro fertilization (IVF) programs employ embryo cryopreservation to enhance pregnancies from a single ovarian stimulation. More embryos are created, some of which are not transferred to the uterus immediately, generating a need for improved cryopreservation protocols. One protocol may involve growing embryos to a further stage of development, allowing only embryos with proven developmental capabilities to be cryopreserved. Here we examined thaw survival, implantation and live birth rates of embryos cryopreserved at different stages.

AIMS:

We examined thaw survival, implantation and live birth rates of embryos cryopreserved at the zygote, day 3 (D3) embryos or blastocyst stage.

SETTINGS AND DESIGN:

This is a retrospective study from a single academic IVF program.

PATIENTS AND METHODS:

A retrospective study of all patients who had frozen embryos transferred to their uteri from year 2002 to 2008 at a single academic IVF program was conducted.

STATISTICAL ANALYSIS USED:

Analysis of variance followed by Fisher's Exact Test was performed to compare the survival after thaw, implantation and live birth rates between the three groups.

RESULTS:

One thousand nine hundred and ninety-one zygotes, 2880 D3 embryos and 503 blastocysts were frozen using a slow freeze technique, thawed and transferred. Significantly more D3 embryos and blastocysts survived the thawing process compared to zygotes and significantly higher implantation rate per number of thawed blastocysts was achieved than that for zygotes. Live birth rates were similar between the three groups.

CONCLUSIONS:

Growing embryos to blastocyst stage prior to cryopreservation is associated with fewer frozen embryos but does not appear compromise patients’ chance of achieving pregnancy

Cryopreservation of blastocysts is the most feasible strategy in good responder patients

OBJECTIVE

To assess on which day to cryopreserve and transfer thawed embryos in good-responder patients by comparing the cycle outcomes of day 3 transfers vs blastocysts formed through extended culture before or after cryopreservation.

DESIGN

Retrospective clinical study.

SETTING

Private IVF center.

PATIENT(S)

Frozen-thawed cycles (n = 2,531) who had ETs at day 3, 5, and 6 and post-thawed extended culture of day 3 until day 5 or 6.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Primary outcomes were implantation and delivery rates. Secondary outcomes were clinical pregnancy and miscarriage rates.

RESULT(S)

In thawing cycles, embryos developing to blastocysts on day 5 through extended culture before or after cryopreservation yielded higher rates of implantation (51.1% and 51.3%, respectively), clinical pregnancy (69.9% and 62.2%, respectively), and delivery per thawing cycle (56.7% and 51%, respectively) accompanied by lower miscarriage rates (15.2%, 16.4%, respectively) compared with day 3 transfers (28.3%, 55.3%, 42.5%, 20.1%, respectively). Late-developing embryos formed before or after cryopreservation resulted in compromised implantation (44.7% and 44.2%, respectively), clinical pregnancy (59.9% and 45.9%, respectively), delivery per thawing cycle (42.8% and 32.4%, respectively) and higher miscarriage rates (25.7% and 23.5%, respectively) than day 5 embryos.

CONCLUSION(S)

The feasible strategy in good responder patients appears to be the cryopreservation of blastocysts in the fresh cycle. Retardation in development results in a compromised outcome because of reduced inherent capacity of embryos.

The Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting

BACKGROUND

Many variations in oocyte and embryo grading make inter-laboratory comparisons extremely difficult. This paper reports the proceedings of an international consensus meeting on oocyte and embryo morphology assessment.

METHODS

Background presentations about current practice were given.

RESULTS

The expert panel developed a set of consensus points to define the minimum criteria for oocyte and embryo morphology assessment.

CONCLUSIONS

It is expected that the definition of common terminology and standardization of laboratory practice related to embryo morphology assessment will result in more effective comparisons of treatment outcomes. This document is intended to be referenced as a global consensus to allow standardized reporting of the minimum data set required for the accurate description of embryo development.

Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting

This paper reports the proceedings of an international consensus meeting on oocyte and embryo morphology assessment. Following background presentations about current practice, the expert panel developed a set of consensus points to define the minimum criteria for oocyte and embryo morphology assessment. It is expected that the definition of common terminology and standardization of laboratory practice related to embryo morphology assessment will result in more effective comparisons of treatment outcomes. This document is intended to be referenced as a global consensus to allow standardized reporting of the minimum dataset required for the accurate description of embryo development. This paper reports the proceedings and outcomes of an international consensus meeting on human oocyte and embryo morphology assessment. An expert panel developed a series of consensus points to define the minimum criteria for such assessments. The definition of common terminology, and standardization of laboratory practices related to these morphological assessments, will permit more effective comparisons of treatment outcomes around the world. This report is intended to be referenced as a global consensus to allow standardized reporting of the minimum descriptive criteria required for routine clinical evaluations of human embryo development in vitro.

Patient selection criteria for blastocyst culture in IVF/ICSI treatment

BACKGROUND

The development and refinement of blastocyst media in recent years has allowed embryos to be cultured in-vitro for 5 or 6 days post oocyte retrieval and has been established as an effective selection tool to aid embryo selection for IVF treatment. It is generally accepted that blastocyst culture is not an appropriate option for all patients but the criteria for patient selection varies between clinics. Our blastocyst culture programme started in February 2005; the patient criteria was set at a minimum of 4 oocytes retrieved, a minimum of 4 2PN pronuclear embryos and at least 4 8-cell embryos of any quality on Day 3 where the female patient was 34 years and under. In the female age group of 35 years and over the criteria was at least 6 oocytes retrieved, a minimum of 6 2PN pronuclear embryos and at least 6 8-cell embryos of any quality on day 3. Improvements in pregnancy rates demonstrated the effectiveness of blastocyst transfer and clinical opinion was that the criteria should be adjusted to allow this option to be available to an increased patient population. From February 2007 the blastocyst patient selection criteria was changed to at least 4 oocytes retrieved, at least 4 2PN pronuclear embryos and at least 2 8-cell and 2 6-cell or 7-cell embryos of top quality on Day 3 in women 38 years and under. For women 39 years and over the criteria was lowered to at least 5 eggs retrieved, at least 5 2PN and at least 3 8-cell embryos and 2 6-cell embryos of top quality on Day 3.

METHODS

Retrospective statistical analysis was carried out to determine the pregnancy rates, live birth rates and twin rate for the period under the initial criteria and to examine the impact that lowering the criteria for patient selection for blastocyst culture had on these parameters.

RESULTS

There was an overall fall in the ongoing pregnancy/live birth rate from 50.9% under the old criteria to 45.0% under the new criteria. However, the patients who had blastocyst culture under the new criteria but would have had day-3 embryo transfer under the initial criteria had a significantly increased live birth/ongoing pregnancy rate from 22.7% to 40.7%. There is an increase in the number of blastocyst culture cycles from 26.4% under the old criteria to 39.1% with the refined criteria. The twin pregnancy rate was reduced from 25.2% to 17.5%.

CONCLUSION

The result of this cohort study revealed that lowering the blastocyst selection criteria may lead to a lower overall clinical live birth rate from blastocyst culture; however, it will benefit a specific group of patients to achieve a better pregnancy and live birth rate. Furthermore, it increases the number of patients who will benefit from the blastocyst culture programme and also reduces multiple pregnancy rate.

Vitrification of in vitro produced ovine embryos at various developmental stages using two methods

This study was conducted to evaluate the effects of developmental stage of in vitro produced (IVP) ovine embryos and the type of vitrification procedure used on embryo cryotolerance. The IVP embryos were vitrified at five different developmental stages: 4-, 8- and 16-cell, morula, and blastocyst. For each stage, half of the embryos were vitrified in either 30 microl 3.4M glycerol+4.6M ethylene glycol in straw (method 1) or in <0.1 microl 2.7 M ethylene glycol+2.1 M Me(2)SO+0.5M sucrose placed on the inner surface of a straw (method 2) of vitrification solution, based on two different procedures. After warming embryo viability was determined by assessing the rates of re-expansion, survival, and blastocyst formation. The quality of surviving embryos was evaluated by their hatching rate and blastocyst cell numbers. In both vitrification methods, embryo survival progressively increased as the developmental stage progressed. In method 1 few of the early cleavage stage embryos (4-, 8- and 16-cell) could reach to the blastocyst stage following warming. There was no significant difference in blastocyst cell numbers (total, ICM, and trophectoderm cells) or hatching rate of blastocysts derived from vitrified embryos at different developmental stages. The number of dead cells in vitrified blastocysts in method 1 was higher than for non-vitrified blastocysts (P<0.05). The number of apoptotic cells in vitrified blastocysts was higher than for non-vitrified counterparts (P<0.05). In conclusion, both the developmental stage of IVP ovine embryos and the method of vitrification have a significant effect on the viability and developmental competence of sheep embryos.

Single Day 2 embryo versus blastocyst-stage transfer: a prospective study integrating fresh and frozen embryo transfers

BACKGROUND

Whether extended culture allowing selection of embryos with high development potential has any advantage over cleavage-stage embryo transfer remains a matter of debate. Among the currently unsolved questions, the cumulative delivery rate resulting from fresh and frozen embryo transfers needs to be taken into account in both strategies. The aim of our study was, therefore, to compare the efficacy of single embryo transfer either on Day 2 or on Day 5/6 combining fresh and frozen embryo transfers.

METHODS

A prospective study including 478 couples assigned on a voluntary basis to undergo elective single embryo transfer (eSET, n = 243) on Day 2 or single blastocyst transfer (SBT, n = 235) on Day 5/6 was performed. The primary outcome measurement was the cumulative delivery rate including fresh and frozen-thawed cycles in both groups.

RESULTS

The delivery rate per cycle following fresh embryo transfer was significantly higher in the SBT group compared with the eSET group (P < 0.01). Conversely, frozen embryo and/or blastocyst transfers tended to result in a higher number of deliveries in the eSET compared with the SBT group. Altogether, the cumulative delivery rate per couple, including fresh and frozen embryo transfers, was similar between the two groups (37.9% versus 34.2% in the SBT and eSET groups, respectively).

CONCLUSIONS

The observed cumulative delivery rates in this study do not allow us to take a position in favor of SBT or eSET. An improvement in blastocyst cryopreservation may change this attitude.

Effect of embryonic fibroblast cell co-culture on development of mouse embryos following exposure to visible light

PURPOSE

To determine the effects of visible light on development of mouse embryos and the potential of fibroblast cells to overcome deleterious effects of visible light on mouse preimplantation stage embryos.

METHODS

Two-cell mouse embryos were randomly allocated to un-exposed group (control) and exposed group receiving 1600 lx visible light for various time lengths. Both exposed and un-exposed embryos were co-cultured with either Mouse Embryonic Fibroblast (MEF) or Human Embryonic Fibroblast (HEF). Developmental rate of embryos at day 3 (morula), 4 (expanded blastocyst) and 5 (hatching or hatched blastocyst) was evaluated.

RESULTS

Exposure of embryos to visible light for 30 min decreased developmental rate significantly (P<0.01). Developmental rate of exposed embryos co-cultured with MEF (58%; p<0.05 both at day 4 and 5) and HEF (67%; P<0.01 both at day 4 and 5) was higher than control.

CONCLUSIONS

Visible light adversely affects embryo development in a time-dependent manner. Feeder cells may enhance embryo development particularly when suboptimal conditions are involved.

Blastocyst culture and transfer: lessons from an unselected, difficult IVF population

Blastocyst-stage transfer has yielded excellent results in good prognosis IVF patients, but its efficacy in the general IVF population has not been clearly demonstrated. The objective of this study was to compare cleavage-stage and blastocyst-stage transfer in a mixed, general IVF population. In a prospective, quasi-randomized study, 152 patients underwent 164 treatment cycles. Patients were allocated to cleavage-stage (group 1; n = 94) or blastocyst-stage (group 2; n = 70) transfer. Main outcome measures included implantation, clinical pregnancy and live birth rates. Implantation (11.2% versus 15.5%), clinical pregnancy (34% versus 21%) and live birth rates per transfer (21.3% versus 13.8%) and per started cycle (21.3% versus 11.4%) were all comparable for groups 1 and 2, respectively. Logistic regression analysis revealed that blastocyst culture and transfer reduced the odds for pregnancy in the general IVF population and defined a good prognosis group for blastocyst transfer. Introducing blastocyst culture and transfer to all IVF patients is not advantageous. Blastocyst transfer should be offered primarily to good prognosis patients, and this group should be specifically defined in each clinical set-up.

An oocyte score for use in assisted reproduction

PURPOSE

In this work, we describe a system for the morphological scoring of human oocytes prior to fertilisation and use this system to test whether oocyte morphology is an indicator of fertilisation, embryo development and implantation potential.

METHODS

The study is a prospective trial of the use of oocyte morphological scores in 822 patients undergoing their first cycle of ICSI. Analyses of oocytes were performed prior to ICSI procedures and the scores compared with fertilisation rates, embryo quality and clinical results.

RESULTS

'Top quality' oocytes had a significantly higher level of fertilisation (96%) as compared to low scoring oocytes (25.6%). Where top quality oocytes formed top quality embryos, we noted a clinical success rate of 63.4%.

CONCLUSIONS

Clinical success rates were increased in cases where top quality oocytes formed top quality embryos after ICSI. The analysis of oocyte morphology may represent a positive selection feature during ICSI.

Successful pregnancy rates achieved with day 4 embryo transfers

OBJECTIVE

To assess the success of day 4 embryo transfers (ETs) following IVF at one institution.

DESIGN

Retrospective analysis.

SETTING

A university hospital IVF program.

PATIENT(S)

Two hundred nondonor, fresh IVF cycles.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE

Outcomes of IVF. Outcome assessments after day 4 ETs included rates of implantation, clinical pregnancy, and singleton and multiple live births.

RESULT(S)

The overall live-birth rate was 54.4%. Implantation rates were highest in younger age groups, and similar in patients 35-40 years of age. Pregnancy and live-birth rates were similar across all age groups up to age 40 years. Multiple gestations were highest in women < or =40 years of age.

CONCLUSION

Acceptable pregnancy rates can be achieved with day 4 ETs.

Comparison of vitrification and conventional cryopreservation of day 5 and day 6 blastocysts during clinical application

OBJECTIVE

To evaluate implantation of day 5 and day 6 vitrified and slow-frozen blastocysts.

DESIGN

Retrospective analysis comparing two cryopreservation techniques.

SETTING

Private IVF clinic.

PATIENT(S)

Five hundred eight cryopreserved embryo transfer candidates.

INTERVENTION(S)

Supernumerary day 5 and day 6 blastocysts were vitrified or slow-frozen and transfered after warming or thawing.

MAIN OUTCOME MEASURE(S)

Comparison of two cryopreservation techniques with respect to survival rate, implantation, and pregnancy rates of day 5 and day 6 blastocysts.

RESULT(S)

In 254 vitrified transfer cycles, survival, embryonic implantation, and clinical pregnancy rates for day 5 blastocysts were 95.9%, 33.4%, 48.7%, respectively, and for day 6 blastocysts 97.5%, 25.9%, 42.8%. In 254 slow-frozen transfer cycles, survival, embryonic implantation, and clinical pregnancy rates for day 5 blastocysts were 91.4%, 29.6%, 42.8%, respectively, and for day 6 blastocysts 94.8%, 28.2%, 43.1%. Overall there was a slightly, but not significantly, higher outcome regarding implantation and clinical pregnancy with the use of day 5 blastocysts (31.3% and 45.4%, respectively) versus day 6 blastocysts (26.7, and 42.9%, respectively).

CONCLUSION(S)

Vitrification technique yields the same implantation and pregnancy rate as slow-frozen blastocyst transfers. Slow growing embryos can be cryopreserved on day 6, because they yield a satisfactory survival, implantation, and pregnancy rate.

Cryopreservation of Human Embryos

Cryopreservation of human embryos from the 2-cell stage up to the morula stage is a safe procedure which has been carried out for the last 25 years. Experience with blastocyst cryopreservation is still limited and pregnancy rates after the use of frozen, thawed blastocysts vary extremely. Vitrification has improved the success of embryo cryopreservation. However, this technique cannot yet be considered as a routine procedure. Despite all of the advantages for infertile couples, cryopreservation of human embryos creates severe ethical problems, because of surplus frozen embryos which either have to be destroyed or perhaps used for research. Embryo adoption may provide a solution to solve imminent medical, ethical and social problems.

Significance of morphological attributes of the early embryo

There are many morphological transformations during development of human embryos that mainly involve phenomena that can be easily assessed in living embryos by simple non-invasive microscopical observation. A clear correlation between pronuclear morphology and the ability of the resulting embryo to continue developing and to implant has been described. There is also general agreement that a positive relationship exists between early embryo morphology and implantation rate. The parameters classically involved in embryo evaluation are: cleavage rate, blastomere symmetry, cytoplasmic appearance, extent of fragmentation and blastomere nuclear status. In this paper, morphological features that have been related to embryo developmental potential are described. Furthermore, the ability of a cumulative classification scheme developed in the laboratory to predict blastocyst formation and implantation is analysed.

Slow controlled-rate freezing of sequentially cultured human blastocysts: an evaluation of two freezing strategies

BACKGROUND

To optimize blastocyst cryopreservation, the prerequisite is to develop a better understanding of factors that influence their survival and implantation potential. Therefore, the aim of the present work was to evaluate, retrospectively, the outcome of blastocyst cryopreservation in a day 2/3 fresh embryo transfer programme.

METHODS

Two different freezing strategies were compared: a first strategy (strategy A: 3007 blastocysts frozen) consisted of freezing those blastocysts that had at least a cavity; a second strategy (strategy B: 3831 blastocysts frozen) consisted of freezing only more advanced stage blastocysts with a good quality inner cell mass and trophectoderm. The outcome of cryopreservation, as related to the two different freezing strategies, was analysed. In addition, after freezing and thawing, we evaluated the influence of blastocyst developmental characteristics on immediate morphological survival and further development in vitro.

RESULTS

The immediate morphological survival after thawing was higher for early blastocysts as compared to advanced and hatching blastocysts. The further developmental potential in vitro of thawed blastocysts was higher for advanced and hatching blastocysts as compared to early blastocysts. As a result, the percentage of deliveries, calculated as a percentage of started thawing cycle, and the percentage of children born, calculated as a percentage of embryos transferred, was not different for strategies A and B.

CONCLUSION

The results clearly indicate that culture conditions and cryopreservation procedures of blastocysts need to be further improved.