Cryopreservation Does Not Affect the Clinical Pregnancy Rate of Blastocysts Derived from Vitrified Oocytes

Vitrified, or "frozen", donor eggs can either be fertilized and cultured for fresh transfer (group 1), or fertilized and cryopreserved for transfer in a "frozen embryo transfer" cycle (group 2). This study compared the pregnancy rates between the two groups. Frozen donor egg cycles (N = 1213) were analyzed at the World Egg Bank. The outcome studied was clinical pregnancy rate. Cycles included only single embryo transfers (ET) without preimplantation genetic testing (PGT). A total of 600 cycles met the inclusion criteria. Group 1 included 409 cycles and group 2 had 191 cycles. There was no statistical significance in clinical pregnancy rate between the two groups (38.63% vs 32.46%, p = 0.14). Mean embryo age was higher in group 2 (5.1 vs. 5.4 days, p < 0.01). The compounding effect of vitrification when applied to two distinct stages (oocyte and embryo), has not been studied. When comparing the two groups, we found no difference in pregnancy rate. However, there was a trend towards fewer pregnancies in group 2. A larger study should be done to determine the validity of this result (Ramadan et al. in Fertil Steril, 2020).