Background <p>The impact of intrauterine exposure to maternal opioid use disorder (OUD) and opioid maintenance treatment (OMT) on child development is not fully understood. This population-based cohort study investigated the neurodevelopmental and behavioral outcomes of four-year-old children prenatally exposed to maternal OMT, hypothesizing greater challenges compared to their same-aged peers in Finland.</p> Methods <p>Children with intrauterine exposure to buprenorphine±naloxone or methadone (<i>n</i> = 123) were compared with typically developing children (<i>n</i> = 434) using standardized language, motor-perceptual, and attention-behavioral skills screening tests. ICD-10 diagnoses for developmental and behavioral disorders were compared with national data from 50,457 Finnish children. Odds ratios (OR) and 95% confidence intervals (CI) were calculated to assess risks.</p> Results <p>Children with prenatal OMT exposure exhibited significantly higher rates of developmental challenges as indicated by screening tests and ICD-10 diagnoses, including speech and language disorders, ADHD, conduct, emotional, and social disorders (F80, F90-94), with <i>ORs</i> ranging from <i>8.97 to 210.21</i>. Additional risk factors included male sex (<i>p</i> &lt; <i>0.001</i>), methadone (<i>p</i> = <i>0.004</i>), illicit drug exposure (<i>p</i> = <i>0.011</i>), and domestic violence (<i>p</i> = <i>0.032</i>).</p> Conclusion <p>Children born to mothers with OUD and OMT face significantly elevated risks of developmental and behavioral challenges. Close monitoring, stable environment and early support for these children with multiple risk factors are crucial.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>This population-based cohort study demonstrates that children with in-utero exposure to maternal OMT are at high risk of neurodevelopmental, emotional and behavioral difficulties at age four.</p> </ItemContent> <ItemContent> <p>Our results particularly add new knowledge of specific domains (skills) in neurodevelopmental screening tests and ICD-10 diagnoses in these children.</p> </ItemContent> <ItemContent> <p>Beyond OMT, multiple additional risk factors such as fetal exposures to illicit substances or other harmful substances and postnatal environmental instability further compound the likelihood of later-life impairments.</p> </ItemContent> <ItemContent> <p>These findings emphasize the critical need for comprehensive follow-up, stable environment, and early interventions for this vulnerable group.</p> </ItemContent> </UnorderedList></p>