Double vitrification and warming does not compromise the chance of live birth after single unbiopsied blastocyst transfer

Double versus single blastocyst biopsy and vitrification in preimplantation genetic testing (PGT) cycles: protocol for a systematic review and meta-analysis of clinical and neonatal outcomes

BACKGROUND

The number of re-biopsied blastocysts is widely increasing in IVF cycles and concerns regarding retesting, which involves double biopsy and vitrification-warming, have been raised. The re-biopsy intervention seems to significantly reduce the pregnancy potential of a blastocyst but the evidence is still restricted to retrospective observational studies reporting a low number of cycles with re-biopsied embryos. Additionally, the neonatal outcomes after the transfer of re-biopsied and re-vitrified embryos are poorly documented to date.

METHODS

A systematic review will be conducted, using PubMed/Medline, EMBASE, Cochrane Central Register of Controlled Trials, Scopus, Web of Science, and Google Scholar to identify all relevant randomized control trials (RCTs), cohort and case-control studies published until December 2024. The participants will include women undergoing preimplantation genetic testing and single euploid frozen embryo transfer (FET) cycles. The primary outcomes are live birth rate (LBR) and singleton birthweight, whereas secondary outcomes are post-warming embryo survival rate, clinical pregnancy (fetal heart pregnancies at 4.5 weeks), miscarriage rate (loss of pregnancy before the 20th week, and stillbirth), preterm birth (PB) rate, small-for-gestational age (SGA, < - 1.28 SDS (standard deviation score)), large-for-gestational age (LGA, > + 1.28 SDS), low birthweight (LBW; birthweight < 2500 g), preterm birth (gestation < 37 weeks), macrosomia (birthweight > 4000 g), pre-eclampsia, eclampsia, perinatal death, and major congenital malformations. Eligible studies will be selected according to pre-specified inclusion and exclusion criteria. Additionally, manual search will target other unpublished reports and supplementary data. At least two independent reviewers will be responsible for article screening, data extraction and bias assessment of eligible studies. A third reviewer will resolve any disagreements. The Newcastle-Ottawa scale (NOS) will be used to assess the quality of the included studies. Studies that receive a score of 7 or higher on the NOS will be considered to have high methodological quality. The extracted data will be pooled and a meta-analysis will be performed. To carry out the data synthesis, a random effects meta-analysis will be conducted using the RevMan software. Heterogeneity will be evaluated by Cochran's Q test and the I2 statistics and the strength of evidence will be rated with reference to GRADE. The review and meta-analysis will be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines.

DISCUSSION

The findings of this systematic review will be important to clinicians, embryologists, patients, and assisted reproductive service providers regarding the decision-making on retesting embryos for PGT in FET cycles.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42024498955.

Does double cryopreservation as well as double biopsy affect embryo viability and clinical outcomes? Evidence from a systematic review of the literature

This study evaluates the effects of double cryopreservation and re-biopsy on embryo viability and clinical outcomes. Studies of interest were selected from an initial cohort of 1027 potentially relevant records retrieved. PubMed was systematically searched for peer-reviewed original papers identified by keywords and medical subject heading terms. Moreover, we elaborated the evidence tables for double cryopreservation and re-biopsy separately. Data were systematically extracted, focusing on live birth, survival, clinical pregnancy, and miscarriage rates. For each study, we identified absolute numbers (numerator and denominator) related to clinical outcomes. Finally, for each outcome, we calculated the percentage change between the control and study groups. Among studies on double cryopreservation, 13 out of 22 reported no effect on clinical outcomes, suggesting contradictory results. Similarly, findings on re-biopsy were controversial, with seven out of 12 studies showing negative effects on survival and clinical outcomes, while five reported no impact. In our analysis of the evidence tables, we observed a reduction in live birth rates of 22.2% and 39.3% in blastocysts undergoing double vitrification and re-biopsy, respectively. These findings suggest that repeated micromanipulations can impair embryo competence. Therefore, double cryopreservation and re-biopsy should be limited in the selected cases without other options by consulting patients about the possible harmful effects.

Embryonic and neonatal outcomes following double vitrification/thawing: a systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis aimed to evaluate the impact of double vitrification/thawing (DVT) versus single vitrification/thawing (SVT) on key embryonic and neonatal outcomes.

DATA EXTRACTION

Information sources included systematic search in PubMed, Scopus, and Cochrane databases up to September 7, 2024. Data from each qualifying study were extracted by two reviewers using a standardized electronic data gathering form.

DATA ANALYSIS

Mantel-Haenszel odds ratio (MHOR) and mean difference (MD) with 95% confidence intervals (CI) were calculated using both fixed and random-effects models. Subgroup analyses were based on biopsy status, number of biopsy rounds, extended culture between rounds of vitrification, and embryo transfer strategy.

RESULTS

A total of 35 studies involving 46,749 embryo transfer cycles were included. After excluding studies that used slow freezing, 28 studies were included in the meta-analyses. The findings indicated that DVT is associated with significant reductions in cryosurvival rates (MHOR: 0.4; CI: 0.3 to 0.8; P < 0.01), biochemical pregnancy (MHOR: 0.7; CI: 0.6 to 0.8; P < 0.01), clinical pregnancy (MHOR: 0.7; CI: 0.5 to 0.8; P < 0.01), and live birth rates (MHOR: 0.6; CI: 0.5 to 0.7; P < 0.01). Additionally, there was a significant increase in the miscarriage rate (MHOR: 1.4; CI: 1.2 to 1.7; P < 0.01). No significant differences were found in neonatal outcomes.

CONCLUSION

Poor-quality evidence suggests that the transfer of double-vitrified embryos might be associated with significantly lower rates of cryosurvival, pregnancy, and live births; however, it does not appear to affect neonatal outcomes such as birth weight and gestational age at birth. Given the small sample size in some subgroups, the high risk of selection, confounding and missing data biases, and the high level of heterogeneity for some outcomes, these findings should be interpreted cautiously.

Vitrification of human blastocysts for couples undergoing assisted reproduction: an updated review

Over the past 40 years there has been a worldwide critical change in the field of assisted reproduction technology (ART), leading to the increased application of single blastocyst transfer, which is extremely important to avoid the risks of multiple pregnancy and associated complications for both mother and babies. Indeed, advancements in ART over the last few decades have been obtained thanks to several improvements, including ovarian stimulation, embryo culture conditions and, of course, progress in cryopreservation methods, especially with the application of vitrification. The ability to cryopreserve human embryos has improved significantly with vitrification compared to the initially adopted slow-freezing procedures. Since the introduction of vitrification, it has become the gold standard method to effectively cryopreserve human blastocysts. However, some new protocols are now being explored, such as the short warming procedure and even shorter exposure to the equilibration solution before vitrification, which seem to provide optimal results. Therefore, the main aim of the current narrative review, will be to illustrate the benefit of vitrification as an effective method to cryopreserve the human blastocyst and to illustrate new protocols and variations which in future may increase the performance of vitrification protocols.