Caesarean sections are often needed when there are complications during a pregnancy or a woman often will elect to undergo a c-section due to a variety of reasons. In some nations, c-section delivery rates are incredibly high and there are attempts to lower these numbers. In Brazil for example, 85% of births in private hospitals are c-section deliveries. Babies born via C-section have been shown to have an increased risk of disease related to immune function. Previous studies had not discriminated against elective or acute c-sections and scientists in Denmark set out to do just that.

Conducting a population based study of 750,569 children born between January 1997 and December 2012, they analyzed children born via elective c-section, acute c-section, and those born vaginally as the reference. They found that the children born by either elective or acute c-section had a higher risk of asthma, laryngitis, and gastroenteritis though electively born c-section babies had a more pronounced risk than acute c-section babies. Those born via elective c-section had an increased risk of lower respiratory tract infection and juvenile idiopathic arthritis. Babies born by acute c-section had an increased risk of ulcerative colitis and celiac disease.

There were other factors not taken into account such as if the children were breastfed or if the mothers had asthma. While not everything was able to be taken into account, with such a large sample size, it is likely that the results from this study would not have been significantly affected by other factors. Most of the effects were seen in diseases that involved the mucosal immune system. The authors believe that the reason for the differences is a result of disturbed immune function as a result of differing microbial colonization in c-section babies.