Previous meta-analyses have found an association between cesarean delivery (CD) and subsequent ADHD in children delivered in that manner. Some have theorized that by bypassing the birth canal, children delivered via CD may acquire their first microbiota from the hospital environment rather than from their mothers, which could disturb the normal development of the nervous system, including the brain.
Nevertheless, earlier studies have not fully explored the role of confounding factors.
A team of Swedish researchers availed themselves of the country's all-encompassing system of national population and health care registers to examine a cohort of over a 1.1 million single births from 1990 through 2003 and followed up through 2013.
They distinguished between planned CD and intrapartum (i.e., during the act of birth) CD. The latter is performed in response to complications with childbirth. This distinction could matter both because of different levels of exposure to the maternal gut microbiota, and because "intrapartum CD is often the result of complications during pregnancy (e.g., preeclampsia) or delivery (e.g., fetal distress), which could affect brain development."
Of 1,179,341 individuals, 1,048,838 were delivered vaginally, 59,514 were delivered by planned CD, and 70,989 were delivered by intrapartum CD.
After adjusting for the child's year of birth, gestational age, age of mother and father at birth, parity, mother's highest education level at birth, maternal smoking during pregnancy, maternal and paternal history of psychiatric disorders, maternal hypertension, maternal diabetes, maternal infections during pregnancy, fetal MAL presentation, large for gestational age, polyhydramnios, oligohydramnios, preeclampsia, and pelvic disproportion, children born by planned CD were 17% more likely to have ADHD.
After adjusting for all previously listed variables plus placenta disorders, dystocia failed induction, and fetal distress, children born by intrapartum CD were 10% more likely to have ADHD.
So far, the analysis confirmed results from previous meta-analyses.
But by exploring such a large cohort, it also became possible to compare ADHD prevalence, not only among unrelated individuals, but also among siblings and cousins, and thereby assess the role of confounders arising from genetics or shared environment.
Whether between full siblings or full maternal cousins, the associations between both types of CD and subsequent ADHD became weak and statistically non-significant.
The authors concluded, "The findings of this study suggest that the association between CD and increased risk of neurodevelopmental disorders in the children was most likely explained by unmeasured familial confounding."
Tianyang Zhang, Gustaf Brander, Ängla Mantel, RalfKuja-Halkola, Olof Stephansson, Zheng Chang, Henrik Larsson, David Mataix-Cols, Lorena Fernández de la Cruz, "Assessment of Cesarean Delivery and neurodevelopmental and Psychiatric Disorders in the Children of population-Based Swedish Birth Cohort,". JAMA Network Open(2020)4(3):e210837,https://doi:10.1001/jamanetworkopen.2021.0837.
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