Risk of Neonatal and Infant Mortality in Twins and Singletons by Gestational Age.

Abstract

To compare neonatal and infant mortality rates stratified by gestational age (GA) between singletons and twins and examine the three leading causes of death among them. This was a retrospective cohort study using the U.S. vital statistics datasets. The study was restricted to nonanomalous live births at 24 to 40 weeks delivered in 2005 to 2014. We used multivariable Poisson regression models with robust error variance to examine the association between birth plurality (singleton vs. twin) and mortality outcomes within each GA, while adjusting for confounders. The results were presented as adjusted risk ratios (aRRs) with 95% confidence intervals (CIs). Of 26,292,747 live births, 96.6% were singletons and 3.4% were twins. At 29 to 36 weeks of GA, compared with singletons, twins had a lower risk of neonatal mortality (aRR: 0.37-0.78) and infant mortality (aRR: 0.54-0.86). When examined by GA, the three leading causes of neonatal and infant mortality varied between singletons and twins. When stratified by GA, the risk of neonatal and infant mortality was lower at 29 to 36 weeks in twins than in singletons, though the cause of death varied.