Vaginal Microbes May Be Transferred After Cesarean Delivery

Lara C. Pullen, PhD

February 03, 2016

Vaginal microbes can be at least partially restored to infants who are delivered by cesarean delivery, according to the results of a pilot study. However, the long-term health consequences of the results remain unclear, researchers caution.

Maria G. Dominguez-Bello, PhD, from New York University in New York City, and colleagues published the results of their pilot study online February 1 in Nature Medicine. The researchers tracked four infants delivered by cesarean delivery who were exposed to maternal vaginal fluids at birth. The researchers determined the composition of their microbiota over time, using more than 1500 samples from anal, oral, and skin sites of infants and mothers in this group and comparator groups during the first month of life.

The investigators found that exposing infants delivered by cesarean delivery to maternal vaginal microbiota results in in bacterial communities that resemble those found on vaginally delivered babies.

"Because [cesarean delivery]–delivered infants were exposed to vaginal fluids through the use of sterile gauzes, we determined how similar the microbiomes of the gauzes were to those of samples obtained from the maternal body sites at day 1. We confirmed that the microbiota of the gauzes that were incubated in the maternal vagina were the most similar to those of the vaginal samples, with both being enriched for Lactobacillus iners," the authors write.

The gauze thus seemed capable of transferring microbes the infant would have encountered during a vaginal birth.

Cesarean Deliveries Disrupt Transfer of Microbes

The microbiota of a newborn mammal is largely determined by delivery through the microbially rich birth canal. Humans are the only mammals that disrupt the exposure of the newborn to the maternal microbiome.

Although cesarean deliveries may be a medical necessity in from 10% to 15% of births, the United States has cesarean delivery rates that are closer to 30%. "Infants born by [cesarean delivery] acquire a different microbiota at birth," explained Dr Dominguez-Bello in a press conference. This difference is associated with immune and metabolic disorders.

Once born, the body sites of the newborn quickly become colonized by microbes seeded from the mother and the environment. The current study found that at birth, neonatal bacterial diversity was highest in the anal and oral sites. Diversity in these areas declined by day 3, and diversity in the skin increased with time.

Although the results of the current study are tantalizing, they are still preliminary. "Labor is, of course, a very complex process," explained investigator Jose C. Clemente, PhD, from the Icahn School of Medicine at Mount Sinai in New York, at the press conference. "Our results establish feasibility, but not health outcomes," he added.

"Of course, the mode of delivery is only one event that contributes to the development of microbiota in the first years of life. The background and clinical history of the mother, the choice for breastfeeding and its duration and exposure to antibiotics are all critical determinants that will need to be carefully controlled in future investigations. Unquestionably, such studies are resource intensive, and randomization will be very challenging," writes Alexander Khoruts, MD, from the University of Minnesota in Minneapolis, in an accompanying News & Views article.

The authors agree. "The final and biggest and most important study, which is very expensive, is the one following babies for years," explained Dr Dominguez-Bello.

The authors and Dr Khoruts have disclosed no relevant financial relationships.

Nat Med. Published online February 1, 2016. Article abstract, News & Views extract

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