Cesarean delivery and Autism

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Children born by cesarean delivery (C-section) appear to have a slightly increased chance of having autism, but the procedure itself does not underlie the association, a new study suggests. More likely, the link stems from environmental and genetic factors that contribute to both the need for a C-section and the likelihood of having autism, but that are difficult to measure.

A possible connection between autism and C-sections has been bandied about for nearly two decades. A 2019 meta-analysis involving more than 20 million people reported that children delivered via C-section were about 30 percent more likely to be diagnosed with autism than those born vaginally.

But the mechanisms behind the link are not clear. Some researchers have proposed that babies who bypass the birth canal are not exposed to essential bacteria that could shape brain development. Others contend that because siblings of children born by C-section are just as likely to be diagnosed with autism, the association is not causal but arises from a shared root.

Fernández de la Cruz and her colleagues analyzed data from a registry of 1,179,341 children born in Sweden from 1990 to 2003: 1,048,838 born vaginally and 130,503 via planned or unplanned C-section. Data from six other registries revealed that 19,030 of the children have autism, 52,257 have ADHD, and 10,332 have intellectual disability.

Children born via planned C-section, typically for medical reasons, were 20 percent more likely to be diagnosed with one of the conditions compared with those who were born vaginally, the team found after controlling for a child’s sex and birth year. Children born via unplanned C-section, which may happen if complications arise during labor, were 17 percent more likely to have one of the conditions.

Those associations remained similar for both groups after controlling for other information, such as the child’s gestational age at birth, the age of the parents, whether the mother smoked during the pregnancy, and whether either parent had a history of psychiatric conditions.

Adding in controls for the mother’s health and possible birth complications, such as hypertension, diabetes, infections and preeclampsia, weakened the association slightly, suggesting that these factors might explain a small portion, but not all, of the link. But children born via C-section were still more likely to be diagnosed with ADHD and intellectual disability, the team found. And children born via a planned C-section were still 20 percent more likely to be diagnosed with autism.

All of the associations disappeared, however, once the researchers included data about siblings, the researchers found. The findings were published earlier this month in JAMA Network Open.