Neurodevelopmental risks of late-preterm and early-term births: a population-based study from Finland

Being born late-preterm and early-term is a known risk factor for neurodevelopmental disorders; however, most studies have focused on intellectual disabilities (ID), autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD), with limited attention to diagnostically distinct disorders of communication or motor development. It remains unclear whether these associations are directly attributed to earlier birth or confounded by shared genetic and environmental factors.

This population-based cohort study included over 1 million singleton children born between 34⁺⁰ and 40⁺⁶ weeks of gestation in Finland during 1996 and 2014, with follow-up for neurodevelopmental disorders through December 2021. Cox proportional hazards models estimated associations between gestational age at birth and risk for neurodevelopmental disorders, adjusting for confounders. Sibling-pair analyses assessed the influence of unmeasured shared familial factors.

Of the cohort, 2.0% were born at 34⁺⁰ to 35⁺⁶ weeks, 7.8% at 36⁺⁰ to 37⁺⁶ weeks, 13% at 38 weeks and 76.5% between 39⁺⁰ and 40⁺⁶ weeks. Prevalence of neurodevelopmental disorders declined with increasing gestational age: 21.6% at 34⁺⁰ to 35⁺⁶ weeks, 19% at 36⁺⁰ to 37⁺⁶ weeks, 16% at 38⁺⁰ to 38⁺⁶ weeks and 15% at 39⁺⁰ to 40⁺⁶ weeks (full-term). Compared with full-term, children born between 34⁺⁰ and 38⁺⁶ weeks had a higher risk of communication disorders, motor disorders and specific learning disorders, with the greatest risks among late-preterm births; risk estimates were similar across sexes. These associations persisted after adjustment for potential confounders, including familial factors shared between siblings. Risks for ID, ASD and ADHD were also observed.

Being born late-preterm and early-term is associated with higher risks of neurodevelopmental disorders. These groups have traditionally received less attention, often being considered at low risk. Our findings underscore the importance of recognising that even late-preterm and early-term births carry measurable neurodevelopmental risk. Promoting longer gestation may support more optimal neurodevelopmental outcomes.