Abstract | Summary | Original Article

Prenatal, perinatal, and neonatal factors associated with Autism Spectrum Disorders

Bilder D, Pinborough-Zimmerman J, Miller J, McMahon W.

Pediatrics 2009; 123(5) May: 1293-1300.

Question: Were there identifiable prenatal, perinatal, and neonatal risk factors for ASD in children born in 1994 in Utah, USA?

Background: In previous studies of risk factors associated with ASD, many conditions or maternal exposures have been proposed. However, no one factor was consistently linked to ASD. Problems with the way in which these studies were carried out limited their ability to identify risk factors. This study used better methods of finding cases of properly diagnosed ASD.

Design: Nested case control study.

Setting: Three counties in Utah, USA.

Participants: Eight-year-old children born in 1994 in 1 of the 3 most populous counties in Utah, all of whom were diagnosed with an ASD. One hundred and thirty-two children were identified and each was matched by sex and year of birth to 100 controls.  

Assessment of Risk Factors: The birth, medical, and school records of these children were assessed for 23 factors such as diseases, conditions, or maternal exposures to toxins or other substances that could be associated with the development of ASD.

Main Outcome Measures: Prenatal factors sought were maternal age, paternal age, first or later born child, prematurity, postmaturity, maternal smoking, infection with genital herpes, high or low levels of amniotic fluid, high blood pressure, uterine bleeding, Rh sensitivity. Perinatal factors were breech birth, mode of delivery (e.g., vaginal, vaginal after previous caesarean, first caesarean, repeat caesarean, forceps, vacuum), early rupture of membranes, fetal distress, or presence of meconium. Neonatal factors were low or high birthweight, normal or low 5 minute Apgar score, infection, respiratory distress syndrome, need for ventilation, birth defect.

Main Results: In this study, the only prenatal factors associated with ASD were advanced maternal age, being the firstborn of a family, and increased number of years of maternal education. Breech presentation was the only perinatal risk factor. There were no significant neonatal factors associated with a diagnosis of ASD.

Conclusions: In this study of 132 children with ASD and 13200 controls, the only risk factors associated with ASD identified were advanced maternal age, being firstborn of a family, increased years of maternal education, and breech presentation at birth. Method of delivery or other birth related factors were not found to be associated with later development of ASD, nor was prematurity, which has been found in other studies.

Bottom Line Many risk factors for ASD have been proposed. In this study, the only risk factors found in a large sample were advanced maternal age, being the firstborn of a family, increased number of years of maternal education, and breech presentation.