The first scientific review of all research on birth-related risk factors for autism has clarified the conditions that may contribute to the development of this neurobiological disorder. The report appears in today’s issue of the journal Pediatrics.
Hannah Gardener and her colleagues at Harvard School of Public Health and Brown University reviewed the scientific literature for clinical studies on birth and newborn conditions that have been associated with autism. They identified 40 individual—and sometimes conflicting—studies suitable for “meta-analysis.” A powerful statistical technique, meta-analysis allows researchers to combine and compare findings across many scientific reports to clarify and strengthen their conclusions.
In doing so, Gardener and her colleagues explored 60 different birth-related conditions suspected as increasing autism risk. These included complications such as prematurity, low birth weight, multiple birth, and birth injury, as well as broader factors such as season of birth.
Specifically, the researchers identified the following complications and conditions as having the strongest association with increased risk that a child will develop autism:
* abnormal birth presentations (e.g. breech),
* umbilical-cord complications (e.g. cord wrapped around neck),
* fetal distress,
* birth injury or trauma,
* multiple birth (twins, triplets, etc.),
* maternal bleeding,
* summer birth (possibly associated with pregnancy during winter flu season),
* low birth weight or small for gestational age,
* physical birth defects,
* low 5-minute Apgar score (a rating of overall newborn health),
* myconium aspiration,
* feeding difficulties,
* newborn anemia or hyperbilirubinemia.
At the same time, the study largely exonerated such risk factors as the use of anesthesia during delivery,
assisted vaginal delivery, post-term birth, high birth weight, and large or small head circumference.
“Importantly the analysis showed that no one birth complication increases risk of autism,” comments Geri Dawson, PhD, chief science officer at Autism Speaks. “Rather it appears that increased risk is associated with a combination of several factors that may reflect what is referred to as suboptimal birth. And even then the risk may only be present when combined with a genetic vulnerability.” Indeed, most children who experience difficult births do not develop autism, she points out.
Of clinical importance, Dawson says, pediatricians can use the study’s findings to better identify at-risk babies and closely monitor their development. In this way, if intervention is needed, therapy can begin early so that children can maximize their progress.
Of additional interest, Dawson notes, many of the factors identified as increasing the risk of autism were associated with hypoxia, or low levels of oxygen in the brain of the baby. “This strong suggestion that low oxygen levels contribute to autism risk needs to be explored in further studies,” she argues.
For more information on the studies that Autism Speaks is funding, explore its science department’s Grants Search portal. For further comment on the Pediatrics meta-analysis study, read the related blog post by Alycia Halladay, Autism Speaks’ director of research for environmental science.