Impact of birth complications on developmental disorders in infants: A longitudinal study

The minutes surrounding birth can shape years of development that follow. This research investigated the longitudinal impact of birth complications on developmental outcomes in infants followed from birth to 36 months in Zurich, Switzerland. A prospective cohort design enrolled 258 infants from the neonatal units and maternity wards of two university-affiliated hospitals between January 2022 and March 2025. Infants were classified by complication severity: no complications (n = 89), mild (n = 74), moderate (n = 58), and severe (n = 37), based on a composite perinatal risk index incorporating gestational age, birth weight, Apgar scores, and neonatal intensive care unit (NICU) duration.Developmental outcomes were assessed at 6, 12, 18, 24, 30, and 36 months using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) across five domains: cognitive, motor, language, social-emotional, and adaptive behavior. Infants with severe complications scored 35.4 points below controls on the composite developmental score at 36 months (64.8 vs. 100.2, p < 0.001). Hypoxic-ischemic encephalopathy (HIE) produced the largest domain-specific deficits, with motor scores averaging 33.7 points below controls. The developmental gap between severe-complication and no-complication groups widened progressively from 6 months (20.5-point difference) to 36 months (35.4-point difference). At 36 months, 62.2% of infants with severe complications met criteria for at least one developmental disorder, compared to 8.9% in the no-complication group (OR = 16.74, 95% CI: 5.82-48.17, p < 0.001). Multiple regression showed that complication severity accounted for 42.3% of variance in 36-month developmental outcomes after controlling for socioeconomic factors. These findings highlight the dose-dependent relationship between perinatal adversity and developmental risk, and support the implementation of systematic follow-up programs for infants with moderate-to-severe birth complications.