C-Section or Vaginal? Baby's Gut Bacteria Linked to Delivery Method

The gut bacteria of 6-week-old babies may be related to the way the infants were delivered and what they have been eating, a new study suggests.

The babies in the study who were delivered vaginally had a different composition of gut bacteria than the babies who were delivered by cesarean section, the researchers found.

Moreover, the babies who had been fed only breast milk since birth had a different composition of gut bacteria at 6 weeks old than the babies who were fed both breast milk and formula, and the babies who were fed only formula, the researchers found.

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"We are actually seeing ... that the gut microbiome of babies who receive formula supplementation to their breast milk really looks more like [the gut microbiome] of babies who have received only formula" than the gut microbiome of babies who are fed only breast milk, said study co-author Dr. Juliette C. Madan, a neonatologist at Children's Hospital at Dartmouth-Hitchcock in Lebanon, New Hampshire. [5 Ways Gut Bacteria Affect Your Health]

In the study, the researchers looked at 102 babies, including 70 who were delivered vaginally and 32 who were delivered by C-section. Of all the babies, 70 were given only breast milk for the first six weeks of life, 26 were fed both breast milk and formula, and six were fed only formula.

When the researchers looked at the composition of the babies' gut bacteria, they found that, for example, bacteria from the group Bacteroides were more abundant in babies delivered vaginally than in babies delivered by C-section. The bacteria from this group are very important for babies because they play a role in developing immunity, Madan said.

Moreover, the babies who were delivered via C-section had elevated levels of bacteria from the group Staphylococcus, and some species of bacteria from this group have been previously associated with disease, said study co-author Anne G. Hoen, an assistant professor of epidemiology at Geisel School of Medicine at Dartmouth College. However, the researchers did not investigate whether the specific bacteria from this group were associated with disease, she added.

When the researchers looked at the composition of gut bacteria in the babies, they also found that the bacterium Lactococcus tended to be present more frequently in the babies who were fed formula alone than in those who were fed breast milk alone. However, it is not clear whether this type of bacteria may play a role in human health, the researchers said.

The researchers noted that they did not examine whether these differences in the composition of gut bacteria translated into actual health outcomes among babies in this particular study.

However, their research may eventually allow them to better understand "how the gut microbiome works with training the immune system and how it relates to health outcomes in general," Madan said.

The new study was published today (Jan. 11) in the journal JAMA Pediatrics.

Follow Agata Blaszczak-Boxe on Twitter. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.