Elective transfer of one embryo is associated with a higher cumulative live birth rate and improved perinatal outcomes compared to the transfer of two embryos with in vitro fertilization

OBJECTIVE: To compare the effects of initial elective single embryo transfer (ieSET) and initial double embryo transfer (iDET) strategies on the cumulative live birth rate (CLBR) and perinatal outcomes after IVF. DESIGN: Retrospective cohort study. SETTING: Society for Assisted Reproductive Technology (SART) reporting clinics. PATIENT(S): 49,333 patients with initial oocyte retrievals between January 2014 and December 2015. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The primary outcome was CLBR, defined as up to 1 live birth resulting from a retrieval cycle and linked transfer cycles. Secondary outcomes included cycles to pregnancy, multifetal delivery rate, infant birthweight, and perinatal mortality rate. RESULT(S): Compared to iDET, ieSET was associated with increased CLBR (74% vs. 57%; adjusted odds ratio [AOR], 1.32; 95% CI, 1.26–1.38). When stratified by age, the same trend was seen in all age categories, with statistical significance for those <38 years of age. ieSET was associated with reduced multifetal delivery (8% vs. 34%; AOR, 0.13; 95% CI, 0.12–0.14), increased birthweight (mean difference, 406 grams; 95% CI, 387–425), reduced preterm births (1.2% vs. 2.8%), and reduced perinatal mortality (0.5% vs. 1.2%). Compared with iDET, ieSET was associated with slightly more embryo transfer cycles (1.7 vs. 1.4 cycles; AOR, 1.19; 95% CI, 1.16–1.21) to achieve a pregnancy resulting in live birth. CONCLUSION(S): The association of ieSET with a higher CLBR and markedly improved perinatal outcomes outweigh the relatively minor increase in time to pregnancy, reinforcing the guidance for eSET in initial transfer cycles, particularly in younger patients with a good prognosis.