Problems and complications that occur during and shortly after childbirth might contribute towards the risk of a child subsequently having autism, researchers from Harvard School of Public Health and Brown university reported in the medical journal Pediatrics.

The authors explained that the causes (etiology) of autism are unknown. However, over the last 40 years there has been some research on what impact perinatal and neonatal exposures might be.

Perinatal – related to the time immediately before and after birth, usually a number of weeks.
Neonatal – related to newborn infants.

Hannah Gardener, ScD and team set out to determine whether there might be a link between perinatal and neonatal factors and autism risk. Their aim was to provide the first review and meta-analysis on the subject.

The researchers gathered data from Pubmed, Embase and Psycinfo – specifically articles on studies that looked at possible associations between autism and perinatal and neonatal factors – up to March 2007.

They selected forty articles which they deemed eligible for the meta-analysis. They used a random-effects model to calculate a summary effect estimate.

They managed to narrow down 60 potential causes to 16 factors with closer links to future autism risk. These factors included:

  • Abnormal presentation
  • ABO or RH incompatibility
  • Birth injury or trauma
  • Congenital malformation
  • Feeding difficulties
  • Fetal distress – abnormal heart rhythm, usually caused by hypoxia (low oxygen). In this case, during labor or just before the baby is born.
  • Hyperbilirubinemia – abnormally high amounts of bile pigment (bilirubin) in the blood.
  • Low 5-minute Apgar score – Apgar measures the physical condition of the newborn with a system of points. It includes heart rate, effort, muscle tone, response to stimulation, skin coloration, and respiration. The top score is 10.
  • Low birth weight
  • Maternal hemorrhage
  • Meconium aspiration – the fetus breaths or sucks in a mass of meconium (green feces)
  • Multiple birth
  • Neonatal anemia
  • Small for gestational age
  • Summer birth
  • Umbilical-cord complications

As many of these neonatal and perinatal factors occur in combination, it is extremely difficult to isolate one on its own and identify it as an autism risk factor, the authors explained.

Assisted vaginal delivery, post-term birth, high birth weight, anesthesia, and head circumference were found not to be linked to subsequent autism risk.

Babies born in the summer months have a 14% higher risk of developing autism compared to those born during other times of the year. The researchers cannot explain why.

The authors concluded:

“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.

This study follows new evidence which suggest that environmental, as well as developmental exposures play a much more significant role in autism incidence than experts had thought. For the last thirty years most doctors and researchers thought that about 90% of autism risk lay in the individual’s genes.

“Perinatal and Neonatal Risk Factors for Autism: A Comprehensive Meta-Analysis”
Hannah Gardener, ScDa, Donna Spiegelman, ScDa,b, Stephen L. Buka, ScDc
Pediatrics July 11. doi: 10.1542/peds.2010-1036

Written by Christian Nordqvist