Geum Joon Cho

Objective To evaluate long‐term adverse neurodevelopmental outcomes of discordant twins delivered at term. Design Retrospective cohort study. Setting Nationwide (Republic of Korea). Population All twin children delivered at term between 2007 and 2010. Methods The study population was divided into two groups according to inter‐twin birthweight discordancy: the ‘concordant twin group’, twin pairs with inter‐twin birthweight discordancy less than 20%; and the ‘discordant twin group’, twin pairs with inter‐twin birthweight discordancy of 20% or more. The risk of long‐term adverse neurodevelopmental outcomes was compared between the concordant twin group and the discordant twin group. Long‐term adverse neurodevelopmental outcomes between smaller and larger twin children within twin pairs were further analysed. The composite adverse neurodevelopmental outcome was defined as the presence of at least one of the following: motor developmental delay, cognitive developmental delay, autism spectrum disorders/attention deficit hyperactivity disorders, tics/stereotypical behaviour or epileptic/febrile seizure. Main Outcome Measures Long‐term adverse neurodevelopmental outcome. Results Of 22 468 twin children (11 234 pairs) included, 3412 (15.19%) twin children were discordant. The risk of composite adverse neurodevelopmental outcome was higher in the discordant twin group than in the concordant twin group (adjusted hazard ratio [HR] 1.13, 95% CI 1.03–1.24). The long‐term adverse neurodevelopmental outcomes were not significantly different between smaller and larger twin children in discordant twin pairs (adjusted HR 1.01, 95% CI 0.81–1.28). Conclusion In twin pairs delivered at term, an inter‐twin birthweight discordancy of 20% or greater was associated with long‐term adverse neurodevelopmental outcomes; and long‐term adverse neurodevelopmental outcomes were not significantly different in smaller or larger twin children in discordant twin pairs.