Within- and between-twin comparisons of risk for childhood behavioral difficulties after preterm birth

Preterm birth and multiple gestation are independently associated with adverse neurodevelopmental outcomes. The objective of this study was to describe risks of screening positive for attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and anxiety in preterm-born twin children by zygosity (monozygotic, dizygotic) and birth order (first-born, second-born).

Caregivers of 349 preterm-born twin pairs (42% monozygotic) aged 3-18 years reported child behavioral outcomes on Strengths and Weaknesses of ADHD Symptoms and Normal Behavior; Social Responsiveness Scale, Second Edition; and Preschool Anxiety Scale or Screen for Child Anxiety and Related Emotional Disorders.

Concordance for behavioral outcomes in twin pairs ranged from 80.06 to 89.31% for ADHD, 61.01 to 84.23% for ASD, and 64.76 to 73.35% for anxiety. Monozygotic twins had a greater risk than dizygotic of screening positive for inattention (risk ratio = 2.91, 95% CI = 1.48-5.72) and social anxiety (1.79, 1.23-2.61). Relative to first-born, second-born twins had a greater risk of screening positive for hyperactivity/impulsivity (1.51, 1.06-2.16); overall ASD (2.38, 1.62-3.49); difficulties with social awareness (2.68, 1.94-3.71), social cognition (4.45, 3.06-6.46), and social communication (2.36, 1.56-3.57); restricted/repetitive behavior (1.91, 1.30-2.81); overall anxiety (1.34, 1.10-1.64); generalized anxiety (1.34, 1.11-1.60); and social anxiety (1.32, 1.06-1.64).

The current findings emphasize considering zygosity and birth order in preterm and multiple birth outcomes research, and highlight clinical implications for discharge planning, neurodevelopmental surveillance, and facilitating parenting and family support.

Zygosity and birth order are important determinants of behavioral and socioemotional outcomes in preterm-born twins. Among 349 preterm-born twin pairs aged 3-18 years (42% monozygotic), 61-89% demonstrated concordance for behavioral and socioemotional outcomes. Monozygosity had greater risks than dizygosity for positive screening of inattention and social anxiety. Second-born twins had greater risks than first-born for hyperactivity/impulsivity, social difficulties (awareness, cognition, communication), restricted/repetitive behavior, and anxiety (generalized, social). These findings have implications for discharge planning, neurodevelopmental surveillance, and facilitating parenting and family support.