More Than Just the Delivery


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See “Mode of Delivery Determines Neonatal Pharyngeal Bacterial Composition and Early Intestinal Colonization” by Brumbaugh et al on page 320.In this issue, Brumbaugh et al (1) describe and compare the oropharyngeal and stool microbiota from 23 mother–infant pairs who undergo different modes of delivery. Approximately half the mothers delivered via C-section and the other half delivered vaginally. The data are based on maternal rectal and vaginal swabs, and infant stool samples. The study was limited to only 6 weeks of follow-up. As a result, it is difficult to draw conclusions on the effect of mode of delivery on long-term intestinal microbial communities; however, some interesting short-term observations emerge.As expected, the study suggests that the delivery mode influences the bacterial communities seen in the initial oropharyngeal inoculum in newborns (2,3). Infants born vaginally had a higher abundance of lactobacilli in the oropharynx, whereas those infants born via C-section had a higher abundance of common skin commensal species, such as Propionibacterium acnes in the oropharynx. The differences between the C-section infants and the vaginal delivery infants are not surprising; however, somewhat unexpected results exist within the group of infants born via vaginal delivery.The stool samples of infants born via vaginal delivery were dissimilar to both the maternal vaginal and rectal swab samples, noted at all time points during the 6-week study. Although the sample size is small, this finding suggests that “infant intestinal bacterial communities are not simply inherited en masse from the mother” (1). In addition, a pattern of gradual succession was noted, with infant born via vaginal delivery demonstrating greater similarity and continuity between successive stool samples.This information should be noted by clinicians who work in birthing centers where parents may ask about new practice fads (4,5). A recent trend for newborn deliveries is the use of “vaginal seeding.” This practice involves swabbing the vagina of women who are about to have a C-section delivery with gauze and then wiping the gauze (with vaginal fluids) on a newborn baby (6). The premise is that this practice allows the newborn infant to inherit the bacteria the infant would have been exposed to in the vaginal canal. This practice theoretically should help reconstitute the intestinal microbiota that would have developed after a vaginal delivery. Randomized controlled trials, however, examining this practice have not yet been reported.The Potential Restoration of the Infant Microbiome (PRIME) is currently underway (NCT02407184) and includes a “vaginal seeding” intervention. In one arm of the study, newborns born in a hospital via standard, planned C-section procedure will be swabbed with gauze containing their mother's vaginal microbiota just after delivery. The primary outcomes of this important study include the bacterial diversity of several body sites on mother and baby (7).It is not known whether “vaginal seeding” is effective; however, until the results of the PRIME study are published, the results from this study by Brumbaugh et al suggest that the development of the infant microbiome and the influence of the method of delivery may be much more complex than simply exposing the infant to fluids from the maternal vaginal canal. Many other factors may play a role and may confound the relation seen between the development of the microbiome and the mode of delivery. These factors include perinatal antibiotic exposure (8), fetal microbial exposure via the placenta (9), early colostrum or breast milk exposure (10), maternal environmental exposures (11), and maternal stress levels (12). For example, C-section is more likely to be associated with maternal antibiotic exposure.

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