Environmental risk factors and biomarkers for autism spectrum disorder: an umbrella review of the evidence

Background: Numerous studies have identified potential risk factors and biomarkers for autism spectrum disorder. We aimed to study the strength and validity of the suggested environmental risk factors or biomarkers of autism spectrum disorder. Methods: We did an umbrella review and systematically appraised the relevant meta-analyses of observational studies. We searched PubMed, Embase, and the Cochrane Database of Systematic Reviews for papers published between database inception and Oct 17, 2018, and screened the reference list of relevant articles. We obtained the summary effect, 95% CI, heterogeneity, and 95% prediction intervals. We examined small study effects and excess significance. We did analyses under credibility ceilings. This review is registered with PROSPERO, number CRD42018091704. Findings: 46 eligible articles yielded data on 67 environmental risk factors (544 212 cases, 81 708 787 individuals) and 52 biomarkers (15 614 cases, 15 433 controls). Evidence of association was convincing for maternal age of 35 years or over (relative risk [RR] 1·31, 95% CI 1·18–1·45), maternal chronic hypertension (odds ratio [OR] 1·48, 1·29–1·70), maternal gestational hypertension (OR 1·37, 1·21–1·54), maternal overweight before or during pregnancy (RR 1·28, 1·19–1·36), pre-eclampsia (RR 1·32, 1·20–1·45), prepregnancy maternal antidepressant use (RR 1·48, 1·29–1·71), and maternal selective serotonin reuptake inhibitor (SSRI) use during pregnancy (OR 1·84, 1·60–2·11). Only two associations, maternal overweight before or during pregnancy and SSRI use during pregnancy, retained their high level of evidence under subset sensitivity analyses. Evidence from biomarkers was scarce, being supported by p values close to the significance threshold and too few cases. Interpretation: Convincing evidence suggests that maternal factors, such as age and features of metabolic syndrome, are associated with risk of autism spectrum disorder. Although SSRI use during pregnancy was also associated with such risk when exposed and non-exposed groups were compared, this association could be affected by other confounding factors, considering that prepregnancy maternal antidepressant use was also convincingly associated with higher risk of autism spectrum disorder. Findings from previous studies suggest that one possible confounding factor is underlying maternal psychiatric disorders. Funding: None.