SynthesisJournal of assisted reproduction and genetics2026
The impact of post thaw embryo culture (extended culture) on frozen embryo transfer outcomes: a systematic review and meta-analysis.
Synthesis in Journal of assisted reproduction and genetics, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
purposeTo systematically evaluate the impact of post-thaw culture duration on frozen embryo transfer (FET) outcomes across different embryonic developmental stages.
methodsWe conducted a systematic review and meta-analysis following PRISMA. A comprehensive search of Medline, Embase, Web of Science, and Cochrane identified 14 eligible studies (N = 17,415) utilizing vitrification. The analysis investigated four post-thaw protocols (extended culture 18-48 h), stratified by embryonic developmental stage: (A) D2ext: day 2 extended vs. day 2 (3 studies, N = 879), (B) D3ext: day 3 extended vs. day 3 (3 studies, N = 11,204), (C) D3-to-D5/6: day 3 extended to day 5/6 vs. day 5/6 (4 studies, N = 1449), and (D) D5/6ext: day 5/6 extended to day 5/6 (4 studies, N = 3883). Pooled relative risks (RRs) with 95% confidence intervals (CIs) and heterogeneity were calculated using random-effects models.
resultsExtended culture significantly improved outcomes for day-3 embryos. D3ext increased live birth rates (RR 1.076, 95% CI 1.034-1.119), while D3-to-D5/6 showed the most pronounced benefit (RR 1.229, 95% CI 1.008-1.499) and reduced biochemical pregnancy loss. Conversely, D2ext showed significantly lower clinical pregnancy rates than immediate transfer (RR 0.689, 95% CI 0.569-0.835). For established blastocysts (D5/6ext), extended culture provided no significant improvement in live birth rates.
conclusionPost-thaw culture strategies should be tailored to embryonic developmental stage. Our most notable finding indicates that day-2 embryos achieve significantly better outcomes with immediate transfer (2-6 h) rather than prolonged in vitro culture. Conversely, day-3 embryos benefit significantly from extended culture (18-48 h), particularly when cultured to the blastocyst stage. Extended culture offers no clinical advantage for embryos already at the blastocyst stage. Post-thaw culture strategies should therefore be strictly tailored to the specific embryonic developmental stage at the time of cryopreservation.
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