Oocyte vitrification in the 21st century and post-warming fertility outcomes: a systematic review and meta-analysis

Oocyte cryopreservation is a rapidly developing technology, which is increasingly being used for various medical, legal and social reasons. There are inconsistencies in information regarding survival rate and fertility outcomes. This systematic review and meta-analysis provides evidence-based information about oocyte survival and fertility outcomes post warming to help women to make informed choices. All randomized and non-randomized, controlled and prospective cohort studies using oocyte vitrification were included. The primary outcome measure was ongoing pregnancy rate/warmed oocyte. Sensitivity analysis for donor and non-donor oocyte studies was performed. Proportional meta-analysis of 17 studies, using a random-effects model, showed pooled ongoing pregnancy and clinical pregnancy rates per warmed oocyte of 7%. Oocyte survival, fertilization, cleavage, clinical pregnancy and ongoing pregnancy rates per warmed oocyte were higher in donor versus non-donor studies. Comparing vitrified with fresh oocytes, no statistically significant difference was observed in fertilization, cleavage and clinical pregnancy rates, but ongoing pregnancy rate was reduced in the vitrified group (odds ratio 0.74), with heterogeneity between studies. Considering the age of women and the reason for cryopreservation, reasonable information can be given to help women to make informed choices. Future studies with outcomes from oocytes cryopreserved for gonadotoxic treatment may provide more insight.