Caesarean section as a risk factor for malformations--a negative finding.

The question whether Caesarean section is a risk factor for malformations was examined among 35,865 children born in 1959-65 and included in the US Collaborative Perinatal Project; 1,407 children were subsequent children of mothers who had a Caesarean section for the previous birth (exposed). The rate of malformed children was about the same in the exposed and non-exposed groups, and the rate of children with major malformations was only slightly higher in the exposed group (risk ratio was 1.1, ie not statistically significant). Multiple variable adjustment for potentially confounding factors further reduced the risk ratios. Caesarean section did not appear to be a risk factor in this population, but further studies covering more recent times and including fetal deaths are needed.