The aetiology of autism is unknown, although prenatal exposures have been the focus of epidemiological research for over 40 years.
In this study managed by the researchers at Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, over 50 prenatal factors were examined.
Also, PubMed, Embase and PsycINFO databases were searched for epidemiological studies that examined the association between pregnancy-related factors and autism. Forty studies were eligible for inclusion in the meta-analysis. Summary effect estimates were calculated for factors examined in multiple studies.
The factors associated with autism risk in the meta-analysis were advanced parental age at birth, maternal prenatal medication use, bleeding, gestational diabetes, being first born v. third or later, and having a mother born abroad.
The factors with the strongest evidence against a role in autism risk included previous fetal loss and maternal hypertension, proteinuria, pre-eclampsia and swelling.