Pregnancy Outcome Difference between Fresh and Frozen Embryos in Women without Polycystic Ovary Syndrome: a Systematic Review and Meta-Analysis

The purpose of this study is to identify that the advantages of frozen embryos are not evident in ovulatory women or women with non-polycystic ovary syndrome (non-PCOS) by meta-analysis. An exhaustive literature search of PubMed (MEDLINE), Embase, and Cochrane Library databases was performed until March 20, 2020 (limited to articles published in English). We included randomized clinical trials comparing the results of frozen and fresh embryo transfers. The primary outcomes were live birth rate and birth weight. The fixed effect model was used when a significant heterogeneity was observed. Otherwise, a random effect model was used. In 511 identified studies, 4 were eligible and were included in this review. There was no difference in live birth rate, singleton birth weight, clinical pregnancy, ongoing pregnancy, gestational diabetes, and gestational hypertension between frozen and fresh embryos. In frozen embryos, the relative risk of moderate or severe ovarian hyperstimulation syndrome (OHSS) was lower, the incidence rate of pre-eclampsia higher, and the standardized mean difference of twin birth weight higher than in fresh embryos. There is no significant difference between frozen embryo transfer (FET) and fresh embryo transfer in ovulatory women or women with non-PCOS. We recommend that the transfer depends on the actual situation in the patient in clinical practice, rather than the “freeze all” policy and thawing FET.