Trends and correlates of the sex distribution among US assisted reproductive technology births

Objective: To assess national trends in the sex distribution of live-born infants in the assisted reproductive technology (ART) and general population and to identify factors correlated with offspring sex. Design: Retrospective cohort study. Setting: Fertility treatment centers. Patients: All live-born infants included in the National Vital Statistics System and resulting from ART cycles reported to the National ART Surveillance System during 2006-14. Interventions: Not applicable. Main Outcome Measure(s): Trends in the proportion of male infants in the general population and proportion of males from fresh ART cycles among all ART live-born infants and singletons after single ET. Result(s): There were 214,274 live-born infants resulting from fresh ART cycles; 53.5% (5,492/10,266) of infants resulting from PGD/PGS cycles were male, as compared with 50.6% (103,228/204,008) in the non-PGD/PGS group. Among non-PGD/PGS cycles, blastocyst transfer was positively associated with male infants (adjusted risk ratio [aRR] = 1.03; 95% confidence interval [CI], 1.02-1.04). Intracytoplasmic sperm injection was negatively associated with male infants (aRR = 0.94; 95% CI, 0.93-0.95) and for singletons after single ET (aRR = 0.93; 95% CI, 0.90-0.95), as was transfer of two embryos (aRR 0.98; 95% CI, 0.97-0.99) or three or more embryos (aRR = 0.98; 95% CI, 0.96-0.99) among all live births from cycles without PGD/PGS use. Conclusion(s): The proportion of male live-born infants among ART population did not change during 2006-14, ranging from 50.5% to 51.2%. Factors such as blastocyst transfer, intracytoplasmic sperm injection use, embryo stage, and number of embryos transferred may be associated with infant sex; further investigation is needed to understand possible underlying causes. ((C) 2019 by American Society for Reproductive Medicine.)