Prematurity and autism: a dose-response relationship across gestational age

OBJECTIVE: To characterize how autism spectrum disorder (ASD) risk varies with gestational age at birth. STUDY DESIGN: We conducted a retrospective cohort study of children born between 2011 and 2023. ASD was identified using ICD-10 codes. Each ASD case (n = 1861) was matched to ten controls using exact and propensity-score matching on sex, birth year, maternal age, ethnic sector, socioeconomic status, and region. Gestational age was grouped into clinically relevant categories, and associations with ASD were evaluated using Fisher's exact test and conditional logistic regression. RESULTS: ASD risk increased progressively with prematurity. Compared with term birth (37-42 weeks), adjusted odds ratios (95% CI) were 1.37 (1.10-1.71) at 36 weeks, 1.67 (1.30-2.15) at 34-35 weeks, 2.14 (1.43-3.18) at 32-33 weeks, 2.95 (1.89-4.59) at 28-31 weeks, and 4.37 (2.26-8.44) below 28 weeks. CONCLUSION: Earlier gestational age is associated with increased ASD risk in a dose-response manner.