Neonatal and Early Childhood Outcomes of Twin and Singleton Infants Born Preterm.

Objective: To compare neonatal and early-childhood outcomes of twins and singletons born preterm and explore the association of chorionicity with outcomes.

Study Design: This was a national retrospective cohort study of singleton and twin infants admitted at 23-28 weeks to level III neonatal intensive care units in Canada (2010-2020). The primary neonatal outcome was a composite of neonatal death or severe neonatal morbidities. The primary early-childhood outcome was a composite of death or significant neurodevelopmental impairment.

Results: The study cohort included 3554 twin and 12 815 singleton infants. Twin infants born at 23-25 weeks had a greater risk of the composite neonatal outcome (adjusted risk ratio 1.04, 95% CI 1.01-1.07). However, these differences were limited to the subgroups of same-sex and monochorionic twin pregnancies. Twin infants of 23-25 weeks were also at an increased risk of the composite early-childhood outcome (adjusted risk ratio 1.22, 95% CI 1.09-1.37). Twin infants of 26-28 weeks were not at an increased risk of adverse neonatal outcomes or the composite early-childhood outcome compared with singleton infants.

Conclusions: Among infants born at 23-25 weeks, twins have a greater risk of adverse neonatal outcomes and the composite early-childhood outcome than singleton infants. However, the increased risk of adverse neonatal outcomes is mostly limited to monochorionic twins and may thus be driven by complications related to monochorionic placentation.