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‘Meta-analysis’ Clarifies Birth Conditions Associated with Autism

July 11, 2011 50 comments

Posted by Alycia Halladay, PhD, director of research for environmental science, Autism Speaks

For over four decades, autism researchers have been combing through birth records to look for events that might increase the risk that a newborn goes on to develop an autism spectrum disorder (ASD). Many clues have emerged regarding the influence of such factors as prematurity, low birth weight, method of delivery, or even the season in which conception or delivery occurs. But no one study was large enough to provide definitive answers, and inconsistent results between studies have caused confusion among scientists as well as parents trying to follow the science.

Today, the respected journal Pediatrics publishes a study that goes far in cutting through the confusion. Researchers from Harvard and Brown universities reviewed and analyzed the combined results of 40 studies that looked at potential autism risk factors during the birth (perinatal) and newborn (neonatal) period.

Such a “meta-analysis” study is a powerful tool in science, as it allows researchers to combine and compare findings from different sources to get a clearer, more reliable picture of the associations between potential risks and conditions such as autism. Importantly, the study confirmed an association between autism and such conditions as abnormal fetal presentation during delivery (for example, breech), fetal respiratory distress (breathing difficulties), birth injury or trauma, low 5-minute APGAR score (a 1-10 score for assessing newborn health after delivery), newborn seizures, low birth weight, multiple births (twins, triplets, etc.), anemia (low blood iron, and being born in the summer.

Of note, preterm birth was not found to be associated with ASD, of particular interest because there had been considerable differences on this count across earlier studies. Most importantly, perhaps, the researchers concluded that the evidence did not implicate any one perinatal or neonatal factor as causing autism by itself. Rather, the evidence suggests that a combination of these factors—reflecting generally poor conditions during and immediately after birth–may increase the risk that a child with an underlying genetic disposition will develop autism.

One common thread across several of these risk factors is that they result in a lack of adequate blood flow to the brain during the birth process. One hypothesis is that, when combined with a genetic predisposition, oxygen deprivation to the brain worsens abnormal brain development. Studying these and other environmental (versus genetic) risk factors for autism is important to increase our understanding of the biology of ASD and to provide practical guidance for physicians and parents on how to avoid or modify those risk factors that can be changed.

In addition, this meta-analysis strongly suggests that pediatricians and parents should closely monitor the development of babies born in difficult situations so that early intervention can be offered should developmental issues such as autism arise. What this study does not say is that difficult birth means a baby will go on to develop autism. Rather, these conditions and complications may increase the risk of autism among those who have a genetic predisposition for developing it.

As in my last post, I want to invite readers to explore the many environmental risk studies that Autism Speaks is supporting with donor dollars, scientific resources, and the participation of autism families in clinical studies. Please see our Grants Search and Participate gateways at www.autismspeaks.org. Thanks for being a vital part of our mission to improve the lives of all who struggle with autism. For more on the Pediatrics meta-analysis study, also see Autism Speaks news.

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