Pregnancy outcomes after warm, biopsy and refreeze cycles of previously untested vitrified blastocysts

Do pregnancy outcomes differ between euploid embryos after warm, biopsy and refreeze (WBR) of previously vitrified blastocysts and euploid blastocysts biopsied before initial vitrification?

All WBR cycles and euploid frozen blastocyst transfers carried out at a single academic institution between 1 January 2014 and 31 December 2021 were included. Pregnancy outcomes were restricted to each patient's first planned euploid frozen embryo transfer (FET). Blastocyst survival was calculated for warming cycles. Pregnancy outcomes were compared between euploid embryos undergoing WBR before transfer and traditional single-warmed euploid embryos.

In total, 295 blastocysts from 50 patients underwent WBR with planned FET. In the control group, 1348 blastocysts from 221 patients underwent trophectoderm biopsy before vitrification. Mean patient age was higher in the controls compared with the WBR group (35.9 versus 32.2 years, P < 0.001). Cumulative blastocyst survival after WBR was 92.5%, reflecting survival across two warming events, compared with 97.4% in the control group, which underwent a single warming before transfer. The odds of biochemical pregnancy (OR 0.85, 95% CI 0.43 to 1.65), clinical pregnancy (OR 1.04, 95% CI 0.54 to 2.00) and live birth (OR 0.86, 95% CI 0.44 to 1.65) did not significantly differ between the groups after adjustment for BMI and endometrial stripe thickness at transfer and age at egg retrieval. Implantation rates per embryo transferred were similar between the WBR and control groups (50.9% versus 48.2%).

Frozen euploid transfers after WBR of previously vitrified blastocysts were not associated with differences in pregnancy outcomes compared with traditional single-warmed euploid transfers. Findings, however, are limited by sample size, retrospective design, potential selection bias in the decision to pursue WBR and lack of long-term obstetric outcomes.