benefits of natural birth vs c-section?

How to give a C-section baby the potential benefits of vaginal birth
New study suggests microbiome can be modified after cesarian section

1 Feb 2016ByJennifer Couzin-Frankel

A new study coats babies born by C-section with the microbes in their mother’s vagina, in an effort to alter the microbial community that’s a part of them. Steve Debenport/iStockphoto
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Babies born vaginally are thought to have an edge over those born via cesarean section. They pick up bacteria from their mother's birth canal, which scientists believe helps protect them from asthma, obesity, and other health issues as they grow older. Now, a new study offers hints that researchers may be able to give these same benefits to C-section babies by "remaking" their microscopic community shortly after birth.

Although the work is extremely preliminary, it's also "a very interesting and simple intervention" that opens up new avenues of exploration, says Dennis Kasper, a microbiologist and immunologist at Harvard Medical School in Boston, who was not involved with the study.

Mothers in labor, like the rest of us, boast a constellation of bacteria all over and in their bodies—what's called the microbiome. Babies born vaginally develop a microbial community that initially resembles that of their mother's vagina, whereas babies who enter the world via C-section have a microbial makeup similar to that of their mother's skin. These differences, in turn, have been associated with increased risks of asthma, allergies, obesity, and immune deficiencies, in human and mouse studies. Exactly how much risk goes up isn't clear, but the studies have caught the attention of many scientists.

This is what makes the next step "so logical," according to Maria Gloria Dominguez-Bello, a microbial ecologist at New York University School of Medicine in New York City: seeing whether the microbiome of a baby born by C-section could be shifted immediately after birth. Dominguez-Bello was especially keen to test this because after 11 years of working in Puerto Rico, she was alarmed by the extraordinarily high C-section rate there, nearly 50%, and in other Latin American countries. "There is this idea that C-section is fine and we don't need to go through labor," she says, and many C-sections are not medically necessary.

So Dominguez-Bello teamed up with computational biologist and microbiome expert Jose C. Clemente of New York City's Icahn School of Medicine at Mount Sinai to launch an unusual clinical trial. They and their colleagues recruited moms scheduled to have a C-section. An hour before the operation, the researchers placed sterile gauze inside the mother's vagina, where it was left until just before surgery began. At that point, the team placed it in a sterile container. Within 3 minutes of the baby's grand entrance, doctors whipped out the gauze and rubbed it all over the newborn's body, starting with the lips and face.

"We know that this is an approximation; we cannot reproduce all the factors that are involved in labor," Clemente says, noting that his own daughter was in the birth canal "for hours." At most, newborns in this study got a minute's rub-down with the bacteria from their mother's vagina.
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Still, the treatment appeared to have an effect. Repeated sampling of bacteria on the skin, in the anus, and in the mouth over the next 30 days revealed a shift toward a typical vaginal microbiome. This was especially true of areas on the skin and mouth. In particular, the researchers report today in Nature Medicine, there was "early enrichment" of Lactobacillus bacteria, followed in week 2 by Bacteroides—two types of healthy bacteria that are noticeably diminished in babies born by C-section. "If you expose a baby to [the] vaginal fluids of his or her mom, bacteria pick up in different places and bloom," Dominguez-Bello says.

But even the authors acknowledge some big caveats. The number of babies in this pilot study was very small: Just four received the gauze treatment, while another seven born by C-section did not. (There was also a comparison group of seven babies born vaginally.) Because there's significant microbiome variation within C-section and vaginal birth groups, a small sample size makes it especially difficult to catch enduring microbiome changes. And there was less difference in anal microbes in the four treated babies than at other sites, when compared with those born by C-section who weren't treated. This suggests the gut may have been less affected than other parts of the body by the gauze experiment, because the bacteria weren't being ingested by the baby as they may be during a vaginal birth. And finally and critically, there's no way to know whether microbiome alterations will have an effect on health down the road.

Dominguez-Bello and Clemente have recruited 86 families to expand the approach, and are hoping to add many more and follow the babies for at least a year.

Even though no one knows whether this strategy will have an effect on health later on—and indeed, the link between C-section and health effects is still just a hypothesis—the approach is so easy that it's tempting to try. Indeed, one of the paper's authors, computational biologist Rob Knight at the University of California, San Diego, applied it to his own daughter when she was born by emergency C-section a few years ago, before the study began. "We took matters into our own hands," he said in a 2014 TED talk, "and made sure she was born with the microbes she would have had naturally."

*Check out our topic page on the microbiome for related information.