title: Perinatal and neonatal risk factors for autism: a comprehensive meta-analysis.
abstract: BACKGROUND
  The etiology of autism is unknown, although perinatal and neonatal exposures have been the focus of epidemiologic research for over 40 years.
  
  
  OBJECTIVE
  To provide the first review and meta-analysis of the association between perinatal and neonatal factors and autism risk.
  
  
  METHODS
  PubMed, Embase, and PsycInfo databases were searched for studies that examined the association between perinatal and neonatal factors and autism through March 2007. Forty studies were eligible for the meta-analysis. For each exposure, a summary effect estimate was calculated using a random-effects model. Heterogeneity in effect estimates across studies was examined, and, if found, a meta-regression was conducted to identify measured methodological factors that could explain between-study variability.
  
  
  RESULTS
  Over 60 perinatal and neonatal factors were examined. Factors associated with autism risk in the meta-analysis were abnormal presentation, umbilical-cord complications, fetal distress, birth injury or trauma, multiple birth, maternal hemorrhage, summer birth, low birth weight, small for gestational age, congenital malformation, low 5-minute Apgar score, feeding difficulties, meconium aspiration, neonatal anemia, ABO or Rh incompatibility, and hyperbilirubinemia. Factors not associated with autism risk included anesthesia, assisted vaginal delivery, postterm birth, high birth weight, and head circumference.
  
  
  CONCLUSIONS
  There is insufficient evidence to implicate any 1 perinatal or neonatal factor in autism etiology, although there is some evidence to suggest that exposure to a broad class of conditions reflecting general compromises to perinatal and neonatal health may increase the risk. Methodological variations were likely sources of heterogeneity of risk factor effects across studies.
authors: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA. hgardener@med.miami.edu
authors: Hannah
authors: H
authors: Gardener
authors: Donna
authors: D
authors: Spiegelman
authors: Stephen L
authors: SL
authors: Buka
mesh_terms: D001321:Autistic Disorder / Q000453:epidemiology* / Q000209:etiology / Q000523:psychology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D015997:Neonatal Screening / Q000379:methods; D018743:Perinatal Care; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology* / Q000503:physiopathology / Q000523:psychology; D012307:Risk Factors