Forty-one additional potential papers were identified after screening the reference lists of original and review articles. demographics, familial psychiatric diseases, genetics, infant behaviors). schizophrenia), and studies of unrelated exposures (e.g. Those studies that were not reviewed included case series, animal studies, autism prevalence studies, medical hypotheses, studies of other psychiatric diseases (e.g. Based on a review of all abstracts, 83 papers were identified as potentially relevant and reviewed further.

The literature search sought to identify all epidemiologic studies that have examined the association of pregnancy and delivery factors and neonatal complications to the risk of autism. The search identified 698 studies in PubMed, 176 in Embase, and 416 in PsycInfo. The PubMed, Embase, and PsycInfo databases were searched using the keywords вЂњautismвЂќ in combination with вЂњprenatalвЂќ or вЂњperinatalвЂќ or вЂњpregnancyвЂќ or вЂњneonatal,вЂќ limited to peer-reviewed studies published in any language through March, 2007. The scope of literature reviewed allows for meta-regression analyses to examine whether study design characteristics explain the heterogeneity in results across studies. We review the evidence for all prenatal factors examined in the literature, and provide a summary effect estimate for all factors examined in two or more studies. Our study expands upon this review by providing the first formal meta-analysis as well as a quantitative review of all 64 studies of prenatal risk factors for autism published through March, 2007. A review article by Kolevson and colleagues discussed seven studies on this topic 9. The purpose of this study is to provide a systematic review and meta-analysis of the epidemiologic literature on the relationship between prenatal complications/exposures and autism. These inconsistencies may be due to methodological variations including diagnostic criteria, comparison groups, sample size, and exposure assessment methods. While many studies support the hypothesis that obstetrical complications may increase the risk of autism 9, the specific complications, magnitude of effect, and overall conclusions of these studies are inconsistent. Pregnancy-related exposures have been the focus of a significant amount of epidemiologic research on possible risk factors for autism. These brain abnormalities suggest that the aetiologically relevant period may be in utero because the pathogenesis may begin during the prenatal period 6. It is now believed that the mechanism underlying autism aetiology is most likely polygenic and potentially epistatic, and that environmental factors may interact with genetic factors to increase risk 6, 7.ДЄlthough the distinctive neuropathology remains elusive, studies have shown macroscopic, microscopic and functional brain abnormalities 6, 8.

Although the estimated 60-92% concordance rate in monozygotic twins as compared to 0-10% in dizygotic twins underscores the importance of genetic influences, the incomplete concordance in monozygotic twins also indicates a role of environmental factors 4, 5. The prevalence of autism has been estimated at 13/10,000 and is believed to be rising 3. Autism is a developmental disorder characterized by deficits in social interaction and communication, and restricted, repetitive interests and behaviors beginning in infancy and toddler years 1, 2.

Comprehensive meta analysis