Maternal Smoking During Pregnancy and Risk of Autism Spectrum Disorder in Offspring: A Systematic Review and Meta-Analysis

Background/Objectives: Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition characterized by persistent social-communication deficits and repetitive behaviors. While genetic factors play a major role, prenatal environmental exposures may also contribute. Maternal smoking during pregnancy is a known risk factor for adverse perinatal outcomes, but its association with ASD remains unclear. Methods: We conducted a systematic review and meta-analysis following PRISMA 2020 guidelines. A comprehensive literature search was performed in PubMed, Embase, Web of Science, Scopus, PsycINFO, and Google Scholar up to September 2025. Eligible observational studies evaluated maternal active smoking during pregnancy and ASD diagnosis in offspring. Effect estimates were pooled using a random-effects model and expressed as relative risks (RR) with 95% confidence intervals (CI). Heterogeneity was quantified using I², with subgroup and sensitivity analyses performed. Results: Twenty-one studies including several million mother–child pairs met inclusion criteria. The pooled RR for ASD associated with maternal smoking was 1.01 (95% CI: 0.95–1.08), indicating no significant association. Subgroup and sensitivity analyses confirmed the robustness of the findings, with no evidence of publication bias. Conclusions: Maternal smoking during pregnancy does not appear to increase ASD risk in offspring. Nevertheless, smoking cessation remains critical due to established adverse fetal effects.