I heard a fascinating edition of NPR’s On Point this week about how the bacteria that colonize our bodies impact our health, influencing everything from digestion to immune functioning (you can listen to the entire show here). The thing I found most interesting about this program was when they discussed how some of the most vital bacteria for promoting healthy development and functioning are acquired during childbirth, specifically through vaginal delivery. The bacterial composition of a woman’s vagina actually changes during pregnancy, presumably to allow certain bacteria to coat the child as it passes through the birth canal. However, if a child is delivered via Caesarean section (or C-section), that child does not have the benefit of being exposed to those bacteria and, as a result, could potentially experience worse health outcomes. After hearing this program, I just had to do some digging to learn more about the research in this area.
The most intriguing study I found examined bacterial communities in several specific anatomic locations of nine mothers and ten infants (four of whom were delivered vaginally and six of whom were delivered via C-section) . Bacterial samples were taken from the mothers shortly before giving birth; the infants were tested within 24 hours of delivery. Perhaps the most important finding was that children delivered vaginally harbored bacterial communities that resembled those found inside their mothers’ vaginas. The specific bacteria shared between these children and their mothers are actually highly beneficial because they assist us in digesting milk and play a role in blood clotting. In contrast, the bacterial communities found in C-section babies tended to be like those found on their mothers’ skin and, therefore, contained fewer of the beneficial bacteria. Although this research is preliminary and based on a very small sample, it does suggest that delivery method may have a big impact on the types of bacteria children acquire.
What are the implications of this for children’s health? There is a significant amount of research indicating that children delivered via C-section tend to have more health problems than children delivered vaginally. For instance, studies have found that children delivered by C-section tend to contract more infectious diseases and have more respiratory infections than vaginally-delivered children . Likewise, children delivered by C-section are twice as likely to become obese as children delivered vaginally, perhaps because C-section babies do not possess the right bacteria in their guts to regulate appetite . Of course, we can’t say with certainty whether bacterial exposure during childbirth is the key factor driving any of these health effects—that link is rather speculative at this point.
Although more work is certainly needed on this topic, the available evidence suggests that method of delivery may have significant implications for children’s health. This should not be taken to mean that C-sections are inherently bad or should never be performed, because C-sections are sometimes a medically necessary and lifesaving procedure. The goal of this article is not to argue for one delivery method over another. However, in cases of “on demand” C-sections (i.e., those that are not medically necessary or are scheduled out of convenience), I think women should be aware of any and all potential health risks to her and her children so that she can make a truly informed decision. Legislators and physicians also need to pay attention to this growing area of research, given the role that malpractice concerns play in doctors’ decisions about which form of delivery to pursue. Some physicians have been sued for failing to perform a C-section in cases where something went wrong with a birth, and these liability concerns have created pressure on doctors to push for more Caesareans than are truly necessary. However, this area of research suggests that unnecessary C-sections may create a whole other set of infant health issues and malpractice worries that will need to be addressed in the future.
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 Dominguez-Bello, M. G., Costello, E. K., Contreras, M., Magris, M., Hidalgo, G., Fierer, N., & Knight, R. (2010). Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proceedings of the National Academy of Sciences of the United States of America, 107, 11971-11975.
 Merenstein, D. J., Gatti, M. E., & Mays, D. M. (2011). The association of mode of delivery and common childhood illnesses. Clinical Pediatrics, 50, 1024-1030.
 Huh, S. Y., Rifas-Shiman, S. L., Zera, C. A., Rich Edwards, J. W., Oken, E., Weiss, S. T., & Gillman, M. W. (in press). Delivery by caesarean section and risk of obesity in preschool age children: A prospective cohort study. Archives of Disease in Childhood.
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