BACKGROUND Elective frozen-embryo transfer has been shown to result in a higher live-birth rate than fresh-embryo transfer among anovulatory women with the polycystic ovary syndrome. It is uncertain whether frozen-embryo transfer increases live-birth rates among ovulatory women with infertility. METHODS In this multicenter, randomized trial, we randomly assigned 2157 women who were undergoing their first in vitro fertilization cycle to undergo either freshembryo transfer or embryo cryopreservation followed by frozen-embryo transfer. Up to two cleavage-stage embryos were transferred in each participant. The primary outcome was a live birth after the first embryo transfer. RESULTS The live-birth rate did not differ significantly between the frozen-embryo group and the fresh-embryo group (48.7% and 50.2%, respectively; relative risk, 0.97; 95% confidence interval [CI], 0.89 to 1.06; P = 0.50). There were also no significant between-group differences in the rates of implantation, clinical pregnancy, overall pregnancy loss, and ongoing pregnancy. Frozen-embryo transfer resulted in a significantly lower risk of the ovarian hyperstimulation syndrome than freshembryo transfer (0.6% vs. 2.0%; relative risk, 0.32; 95% CI, 0.14 to 0.74; P = 0.005). The risks of obstetrical and neonatal complications and other adverse outcomes did not differ significantly between the two groups. CONCLUSIONS The live-birth rate did not differ significantly between fresh-embryo transfer and frozen-embryo transfer among ovulatory women with infertility, but frozenembryo transfer resulted in a lower risk of the ovarian hyperstimulation syndrome. (Funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China; Chinese Clinical Trial Registry number, ChiCTR-IOR-14005406.).
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