Live-birth rates similar among ovulating women undergoing fresh- or frozen-embryo transfer

1. No differences were observed in live-birth rate, rates of implantation, clinical pregnancy, overall pregnancy loss, or ongoing pregnancy incidents between ovulatory women with infertility who received frozen-embryo or fresh-embryo transfers.

2. Frozen-embryo transfer resulted in significantly lower rates of ovarian hyperstimulation syndrome compared to fresh-embryo transfer.

Evidence Rating Level: 1 (Excellent)

Study Rundown: In vitro fertilization (IVF) has progressed rapidly since its introduction into clinical practice. Frozen-embryo transfer has shown promise as a superior method of IVF compared to fresh-embryo transfer, demonstrating higher live-birth rates and lower rates of pregnancy loss in small-scale observational studies. This randomized control trial compared frozen-embryo to fresh-embryo transfer among a cohort of normally ovulating women with infertility to assess for differences in the primary outcome of live-birth rates and secondary pregnancy outcomes. Overall, there were no significant differences noted in live birth-rates, obstetrical or neonatal complications, or mean birth weight between the two groups. Notably, women randomized to receive frozen-embryo transfer had lower rates of ovarian hyperstimulation syndrome compared to women who received fresh-embryo transfers.

Click to read the study, published today in NEJM

Click to read an accompanying editorial in Reproductive Biology and Endocrinology

Relevant Reading: Fresh versus frozen embryos for infertility in the polycystic ovary syndrome

In-Depth [randomized controlled trial]: This multicenter, randomized controlled trial enrolled 2157 ovulatory women with infertility to undergo either frozen-embryo or fresh-embryo transfer in a 1:1 block randomization pattern. Participants in this trial were ages 20 to 35, had a normal menstrual cycle, and were undergoing their first cycle of IVF as a result of tubal factors, male factors, or both. The primary outcome was live birth rates after participants’ first transfer, as defined by birth of a viable neonate on or after 28 weeks of gestation. Secondary outcomes included rates of pregnancy complications (ovarian hyperstimulation syndrome, ectopic pregnancy, congenital anomaly), birth weight, rates of pregnancy loss, and comparisons of biochemical pregnancy and clinical pregnancy characteristics.

There were no significant differences in the live-birth rate between the frozen-embryo group and the fresh-embryo group (48.7% and 50.2%, respectively; relative risk, 0.97; 95% confidence interval, 0.89 to 1.06; p = 0.50). There were no differences observed between treatment groups in mean birth weight or rates of implantation, ongoing pregnancy or overall pregnancy loss. A lower rate of pregnancy loss in the 2nd trimester was observed in the frozen-embryo (1.5%) group compared to the fresh-embryo (4.7%) group (RR, 0.33, 95% CI; 0.16 to 0.68; p = 0.002). A lower risk of ovarian hyperstimulation syndrome among women in the frozen-embryo group was detected (0.6% frozen-embryo vs 2.0% fresh-embryo; RR, 0.32, 95% CI; 0.14 to 0.74; p = 0.0005).

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