That such stressful and expensive surgery is being carried out more often than necessary is a concern. However, more recently, a second worry has emerged. This is that a cesarean section prevents infants picking up, from their mother's vagina and perineum, bacteria that establishes itself in a newborn's gut, and improves its future health.
Gathering evidence suggests that cesarean babies are more prone to allergies, autoimmune diseases, and obesity. A study by Dr. Maria Dominguez-Bello from the New York School of Medicine, which was published recently in Science Advances, takes a look at the latter.
There is a well established connection between obesity and the type of bacteria living in someone's gut, and thus this seems the likely explanation for the link between cesareans and obesity. This can come about in one or two ways: Either the procedure keeps bacteria and baby apart or the bacteria are killed by the antibiotics which are used during the surgery.
To see what was more likely to be the case, Dr. Dominguez-Bello carried out some experiments using mice. She allowed some pregnant mice to give birth naturally and performed antibiotic-free cesareans on others. She then raised the babies in identical conditions.
Her sample size was small - 13 pregnant females produced 69 offspring, of which 35 were born naturally and 34 were delivered by cesarean. However, her results were pretty conclusive.
At 15 weeks old, the mice that had been delivered naturally weighed around 39 grams, while the cesarean-delivered kin averaged 45 grams. The probability of this difference resulting from chance is less than 1 in a 1,000. To add to this, when she examined the gut bacteria of the mice she found that those which were born naturally had a normal mixture while those born via cesarean lacked Clostridiales, Ruminococcaceae, and Bacteroides. These are all bacteria groups associated with lean bodies.
Therefore, it seems that in mice - and by extension presumably human women - it is the operation itself rather than the associated antibiotics that are promoting bacteria-mediated obesity. Fortunately, as Dr. Dominguez-Bello points out, this should be an easy issue to fix. She is now experimenting with taking a swab of the mother's vagina and wiping it on the infant's face shortly after a cesarean birth to try pass on the relevant bugs. This might sound distasteful, but if it works it will help give cesarean babies a better start in life.