Association between gestational age and child health and neurodevelopment in twins from a nationwide longitudinal survey in Japan.

Despite previous research, evidence on the relationship between gestational age and long-term health and neurodevelopmental outcomes among twins remains limited. Using data from the Longitudinal Survey of Babies in the 21st Century, we analyzed 549 twins born in Japan in 2010. The twins were grouped by gestational age: <32 weeks (very preterm), 32-36 weeks (moderately and late preterm), and 37-38 weeks (early term). The health status was evaluated by hospitalization between 0.5 and 5.5 years, and behavioral development was assessed using questionnaires at 2.5 and 5.5 years. Binomial log-linear regression with generalized estimating equations accounted for within-pair correlations and adjusted for child and parental variables. Moderately and late preterm children showed a higher risk of all-cause hospitalization during infancy than early-term children (adjusted risk ratio, 1.7; 95% CI, 1.0-2.6). Very preterm children showed a higher point estimate of the risk ratio, but a wide CI (risk ratio, 2.3; 95% CI, 0.8-6.8). Behavioral delays were more common in preterm groups at 2.5 years but not at 5.5 years. Preterm twins have a higher risk of hospitalization during infancy and developmental delay at 2.5 years than early-term twins. These risks show an increasing trend as gestational age decreases.