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Largest-ever study of autism & C-sections suggests shared triggers

Analysis of 2.7 million births suggests that cesareans don’t cause autism, but both may share underlying risk factors
June 23, 2015

The largest-ever study of a suspected link between cesarean delivery and autism confirms an association but suggests that it’s due to a shared trigger. In other words, the C-section procedure itself does not appear to increase the risk that a child will develop autism. Rather, one or more common, underlying factors may increase the likelihood for both.

The findings appear online today in the medical journal JAMA Psychiatry.

“While this study supports earlier findings of an association between cesarean and autism risk, it adds important information to the picture,” comments epidemiologist Michael Rosanoff, Autism Speaks director for public health research.

The researchers analyzed the health records of more than 2.7 million Swedish children. This included 13,411 pairs of siblings in which only one had autism and 2,555 sibling pairs where one was born by cesarean and the other by unassisted vaginal delivery.

Confirming the results of smaller studies, the researchers found that, overall, autism rates among children born by cesarean were around 20 percent higher than that of children born by unassisted vaginal delivery. This was after controlling for possible confounding risk factors such as extreme prematurity.

The researchers then went further – to look at differences between the sibling pairs. They found no significant difference in C-section rates between those who developed autism and those who did not.

As a result, the authors conclude, “It is more likely that birth by cesarean section is related to some unknown genetic or environmental factor that leads to increased risk of both [autism and C-section].”

For example, a fetus with developmental issues may have low muscle tone that can interfere with moving into proper position for natural delivery. In this and other ways, the fetus plays a crucial role in initiating and advancing natural labor, explains developmental pediatrician Paul Wang, Autism Speaks head of medical research.

“The findings are reassuring since cesarean section is often a life-saving procedure for both mother and child,” Dr. Wang adds. “At the same time, it underscores how crucial it is that women receive optimal healthcare including well-pregnancy care, beginning before conception and through delivery.” 

For related research news, also see:

CDC study supports link between autism and pregnancy problems

Avoiding toxic exposures during pregnancy

Prenatal folic acid reduces autism risk

Study finds moderate exercise during pregnancy promotes newborn brain development