Single and double embryo transfer provide similar live birth rates in frozen cycles

Research question: Do live birth rates (LBRs) differ in frozen cycles of women who received single versus double embryo transfer?Design: Retrospective cohort study including women who underwent their first frozen embryo transfer (FET) in a tertiary referral University Hospital between 2009-2014.Results: 3601 patients were included in the analysis with 1936 (53.8%) having a single embryo transfer (SET) and 1665 (46.2%) having a double embryo transfer (DET). Overall, 657/3601 (18.24%) had a live birth. LBR were similar between SET and DET either for cleavage [100/757 (13.1%) versus 153/1032 (14.8%), p = .33] or blastocyst stage FET [256/1179 (21.7%) versus 148/633 (23.4%), p = .4). Ongoing pregnancy rates were comparable between DET and SET [316/1665 (18.9%) versus 359/1936 (18.5%)]. Multiple delivery rates were significantly higher in women with DET compared to SET [53/316 (16.7%) versus 7/359 (1.9%), p < .001]. Multivariate logistic regression analysis allowing adjustment for relevant confounders showed that the number of embryos transferred in the frozen cycle was not related to LBR.Conclusions: This is the largest study providing evidence that both SET and DET may result in similar LBR, albeit multiple pregnancy rates are significantly lower in case of SET. Therefore, SET should be the main strategy in women undergoing FET.