On the safety of vaginal microbial transfer in C-section infants and expected health outcomes
In the recent editorial by Cunnington et al. (“Vaginal seeding” of infants born by caesarean section. BMJ 2016;352:i227), the authors acknowledge the epidemiological associations between birth by Caesarean delivery and increased risk of obesity, asthma, and autoimmune diseases. These risks are also increased by alterations of the microbiota during early development. The authors also indicate that Caesarean-delivered newborns exhibit an unnatural microbiota composition, as demonstrated by us and others1,2, and state that “in theory, vaginal seeding might restore the microbiota of infants born by Caesarean section to a more “natural” state and decrease the risk of disease”, but that benefits of this practice now called “seeding” have not been proved. The authors warn against its widespread use without proper testing due to the risk of infections from exposure to vaginal commensals and pathogens, which the mother may carry asymptomatically.
Although we agree with Cunnington and colleagues in that risks are associated with the transfer of vaginal bacteria to the newborn, we would like to make the following clarifications:
1- As acknowledged in the editorial, the composition of the early microbiota of infants delivered by Caesarean is unnatural, resembling that of human skin instead of the vaginally acquired normal microbiota present in infants born naturally1,2.
2- We have demonstrated that the microbiota of Caesarean-delivered newborns is partially normalized during the first month of life if the newborn is exposed to maternal vaginal fluids3. As we indicate in our publication, the expected health restoration of the procedure has not been assessed yet, and we agree that this is a critical study to pursue.
3- Despite the infection risks that the authors correctly associate with our procedure, vaginal birth is the desired mode of delivery after a healthy pregnancy even in the case of GBS-positive mothers, which in the US are treated with antibiotics to deliver vaginally. Infection risks are acknowledged in our study3 and led us to the use of inclusion criteria (negative GBS test, no evidence of viral or bacterial infections, and acidic vaginal pH) stricter than the current standards for vaginal delivery.
4- We fully agree with the authors in that breast feeding should be encouraged and unnecessary antibiotics and Caesarean sections should be avoided.
More studies are needed to determine the health benefits of the multiple factors that shape microbial composition in infants, such as transfer of vaginal bacteria, breast feeding, and limited antibiotic usage. Interventions that alter natural processes such as vaginal birth should be practiced only when necessary, and the results of our study are a first step towards reducing the potential health costs associated with C-section.
Maria G. Dominguez-Bello, Ph.D.
Jose C. Clemente, Ph.D.
1. Dominguez-Bello MG, Costello EK, Contreras M, et al. Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci U S A. 2010;107(26):11971-11975.
2. Backhed F, Roswall J, Peng Y, et al. Dynamics and Stabilization of the Human Gut Microbiome during the First Year of Life. Cell Host Microbe. 2015;17(6):852.
3. Dominguez-Bello MG, De Jesus-Laboy KM, Shen N, et al. Partial restoration of the microbiota of cesarean-born infants via vaginal microbial transfer. Nature Medicine. 2016.
Competing interests: New York University has filed an U.S. patent application (number 62161549) on behalf of Maria G. Dominguez-Bello, related to methods for restoring the microbiota of newborns. Jose C. Clemente declares no competing interests.