Adherence to embryo transfer guidelines in favorable-prognosis patients aged less than 35 years using autologous oocytes and in recipients using donor oocytes: a Society for Assisted Reproductive Technology Clinic Outcome Reporting System study

Objective: To measure the consequences of nonadherence with the 2013 American Society for Reproductive Medicine elective single embryo transfer (eSET) guidelines for favorable-prognosis patients. Design: Retrospective cohort. Setting: In vitro fertilization clinics. Patient(s): A total of 28,311 fresh autologous, 2,500 frozen-thawed autologous, and 3,534 fresh oocyte-donor in vitro fertilization cycles in 2014–2016 at Society for Assisted Reproductive Technology-reporting centers. Intervention(s): Patients aged <35 years or using donors aged <35 years underwent first blastocyst transfer. Main Outcome Measure(s): Singleton birth rate, gestational age at delivery, and birth weight were compared between the eSET and non-eSET groups using the chi-square or Fisher's exact test or t-tests. Result(s): Among fresh transfers, 15,643 (55%) underwent eSET. Live births after non-eSETs were less likely singletons (38.0% vs. 96.5%; adjusted relative risk [aRR], 0.56) and more likely complicated by preterm delivery (55.0% vs. 20.1%; aRR, 2.39) and low birth weight (<2,500 g) (40.1% vs. 10.6%; aRR, 3.4) compared with those after eSET. Among frozen-thawed transfers, 1,439 (58%) underwent eSET. Live births after non-eSETs were less likely singletons (41.9% vs. 95.2%; aRR, 0.69; 95% confidence interval, 0.66–0.73) and more likely complicated by preterm delivery (56.4% vs. 19.5%; aRR, 2.6; 95% confidence interval, 2.2–3.1) and low birth weight (38.0% vs. 8.9%; aRR, 3.9) compared with those after eSET. Among fresh donor oocyte transfers, 1,946 (55%) underwent eSET. Live births after non-eSETs were less likely singletons (31.3% vs. 97.3%; aRR, 0.48) and more likely complicated by preterm delivery (61.1% vs. 25.7%; aRR, 2.09) and low birth weight (44.3% vs. 11.7%; aRR, 3.39) compared with those after eSET. Conclusion(s): Nonadherence with transfer guidelines was associated with dramatically increased multiple pregnancies, preterm births, and low birth weights.