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Cesarean section may increase risk for autism diagnosis

Children born by cesarean section are approximately 20% more likely to be diagnosed with autism spectrum disorder, according to data published in JAMA Psychiatry.

“Although [autism spectrum disorder] is highly heritable, it has previously been linked to numerous perinatal factors, possibly including birth by cesarean section. There are several possible mechanisms underlying this association, including early-term birth, exposure to altered microbiota, change in stress response and type of anesthesia,” according to study researcher Eileen A. Curran, MPH, of Cork University Maternity Hospital in Cork, Ireland, and colleagues.

Researchers assessed data from the Swedish Medical Birth Register and the Swedish National Patient Register for all singleton live births in Sweden from January 1982 through December 2010. The cohort included 2,697,315 children, of which 28,290 (1%) were diagnosed with autism spectrum disorder (ASD). Children were followed until first diagnosis of ASD, death, migration or Dec. 31, 2011.

Median age at ASD diagnosis was 12 years.

Eighty percent of the study cohort was born by via non-assisted vaginal delivery, 7.3% via assisted vaginal delivery, 6.5% via emergency cesarean section and 6.1% via elective cesarean section.

When adjusting for birth year, elective cesarean section (HR = 1.39; 95% CI, 1.33-1.45), emergency cesarean section (HR = 1.4; 95% CI, 1.34-1.46) and assisted vaginal delivery (HR = 1.18; 95% CI, 1.13-1.23) were associated with increased risk for ASD diagnosis when compared with unassisted vaginal delivery.

Full adjusted analysis showed lower hazard ratios, but the association was still significant for elective cesarean section (adjusted HR = 1.21; 95% CI, 1.15-1.27) and emergency cesarean section (aHR = 1.15; 95% CI, 1.1-1.2).

Researchers conducted a sibling control study, in which there were 13,411 sibling pairs discordant on ASD. Assisted vaginal delivery and elective cesarean section were not associated with ASD when adjusting for birth year or in full adjusted analysis using this cohort.

Although emergency cesarean section was associated with ASD when adjusting for birth year (OR = 1.2; 95% CI, 1.06-1.36), it was not in fully adjusted analysis (OR = 0.97; 95% CI, 0.85-1.11).

“Although the traditional cohort analysis revealed birth by [cesarean section] to be associated with ASD, it is not necessarily a cause because the association could be due to residual confounding,” Curran and colleagues wrote. “Therefore, because the association between birth by [cesarean section] and ASD did not persist in the sibling control analysis, we can conclude that there is no causal association. 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 [cesarean section] and ASD.” – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.