The effect of incubation period after warming on reproductive outcomes of frozen single blastocyst transfer

Does the duration of incubation after warming between thawing and embryo transfer affect reproductive outcomes in IVF patients? 1856 single frozen blastocyst transfer cycles from January 2021 to December 2021 were analyzed. And were divided into two groups, 1704 Group A (or “Day Before”), in which blastocysts were warmed on the day before transfer, cultured for approximately 18 hours (range 16–22 hours), and then transferred. And 152 group B (or “ET-Day”), in which embryos were warmed on the day of transfer, kept in culture during approximately 4 hour, and then transferred. IVF cycles using donor oocyte, TESE sperm, PGT, or those lacking follow-up were excluded. For group A, if the blastocyst had not re-expanded or degenerated prior to embryo transfer, additional warming was performed when possible. All women underwent standard IVF protocols following usual individualized practice in our IVF clinic. All blastocyst transfers were performed under ultrasound guidance during an ovulatory or a hormonal replacement therapy (HRT) cycle. The clinical pregnancy rate and pregnancy rate of cryopreserved embryos transferred after overnight culture was significantly higher than after 4 hours culture after thawing. (56.9% vs. 39.5% p<0.05, 67.0% vs. 48.5% p<0.05 ) The ongoing pregnancy rate was also higher in group A, but there was no significant difference. (48.9% vs. 31.6% p>0.05) Cryopreserved embryos transferred after overnight cultureafter thawing provided a better success rate than culture after 4 hours culture after thawing.