Reconsideration of the safety and effectiveness of human oocyte cryopreservation

Mature oocyte cryopreservation (OC) has become increasingly common since the American Society for Reproductive Medicine declared OC to no longer be experimental. Utilization of the open vitrification protocol has led to a marked improvement in the efficacy of oocyte cryopreservation. However, the safety and effectiveness of this cryopreservation method remain controversial. A previous report stated that among all initiated recipient cycles, the live-birth rate among recipients of all ages was significantly higher when using fresh donor oocytes (FDOs) rather than cryopreserved donor oocytes (CDOs). Confounding patient characteristics were noted as possible causes. OC stands as an acceptable elective medical intervention for preserving fertility in women. To further understand the effects of OC on the live birth rate resulting from fresh versus cryopreserved donor oocytes, reported data from the Society for Assisted Reproductive Technology from 2013 to 2020 were analyzed. The mean of the mean live-birth rate in all ages resulting from FDOs was 49.0% (44.6–53.3%) versus 41.0% (39.1–43.2%) for CDOs (difference, 8.0% [95% confidence interval, 5.35–10.57%], p value < 0.001). The lower live-birth rate observed for CDOs versus FDOs has been consistent throughout past decades. While there has been no reported increase in the aneuploidy rate for CDOs compared to FDOs, differences in the nondisjunction separation rate among different chromosomes were described in a recent report. Open vitrification culture medium usually contains high concentrations of cryoprotectants, such as 15% dimethyl sulfoxide (DMSO) and 15% ethylene glycol (EG). Recent studies showed that tissue culture with 0.1% DMSO or 10% EG resulted in deregulation of gene expression, disruption of epigenetic imprints, and accumulation of reactive oxygen species. The addition of melatonin, which can remove reactive oxygen species from vitrification medium, was shown to improve CDOs qualities and functions to conditions similar to those of FDOs; however, there were insufficient data to conclude that melatonin could improve the lower live-birth rate. These factors that affect live birth rates, birth defects, birth weights and developmental health cannot be ignored and perhaps need to be studied again and followed when evaluating the true effectiveness of human oocyte cryopreservation.