Earlier studies have shown that delivery by cesarean section (CS) is associated with an increased risk of disease associated with immune function in the offspring, but these studies have generally not discriminated between the effect of acute and elective CS.

We sought to further explore these associations using discrimination between the effects of acute versus elective CS.

We performed a population- and national register–based cohort study including all children born in Denmark from January 1997 through December 2012. Hazard ratios for diseases associated with immune function in children delivered by acute and elective CS with vaginal delivery as the reference were calculated by using Cox regression. All analyses were adjusted for gestational age, sex, birth weight, maternal age, maternal smoking during pregnancy, and complications during pregnancy (preeclampsia, eclampsia, hemorrhage, and hyperemesis).

A total of 750,569 children aged 0 to 14 years were included. Children delivered by both acute and elective CS had an increased risk of asthma, laryngitis, and gastroenteritis. Children delivered by acute CS had an increased risk of ulcerative colitis and celiac disease, whereas children delivered by elective CS had an increased risk of lower respiratory tract infection and juvenile idiopathic arthritis. The effect of elective CS was higher than the effect of acute CS on the risk of asthma.

Children delivered by CS are at increased risk of disease associated with immune function. The effect is mainly on diseases involving the mucosal immune system.