Infant Microbiome Similar With Cesarean or Vaginal Delivery

Marlene Busko

February 01, 2017

Among infants 6 weeks of age, researchers found no substantial difference in microbiome diversity or pattern among those born via vaginal or cesarean delivery, according to a prospective study.

"We conclude that within the first 6 weeks of life, the infant microbiota undergoes substantial reorganization, which is primarily driven by body site and not by mode of delivery," Derrick M. Chu, a student in the Medical Scientist MD/PhD training program at Baylor College of Medicine, Houston, Texas, and colleagues write in an article published online January 23 in Nature Medicine.

Shifts in microbial communities have been associated with obesity, inflammatory bowel disorders, autoimmune disease, and gastrointestinal cancer, the authors note; thus, it is important to find out more about how host–microbial symbiosis is established and maintained in early life.

Caesarian deliveries, which are common worldwide, might be tied to allergic and autoimmune disease, as the infant would not be exposed to bacteria in the mother's vaginal canal during birth.

This study of 162 pregnant women and their newborns used whole-genome shotgun sequencing and sequencing analysis of the gene encoding 16s rRNA to determine bacterial composition and function at multiple body sites; it found no evidence of negative effect on the microbiome in infants born via cesarean surgery.

Whereas some experts have suggested that these new data refute the idea that cesarean delivery adversely affects an infant's microbiome, senior author Kjersti M. Aagaard, MD, also from Baylor College of Medicine, sees the discussion a bit differently.

"[F]rom our perspective, we have not refuted others work, and that was never the intent of our study," she told Medscape Medical News. "Rather, our observations differ from some work of others (but not all) insomuch as we fail to demonstrate a distinct difference in the infant microbiome by virtue of mode of delivery at 4 to 6 weeks of age."

She also notes that the current study differs methodologically from previous ones. For example, some other studies only looked at the microbiome at the time of delivery or only observed a difference at 1 or 2 years of age or greater, or not at all.

Moreover, Dr Aagaard's team looked at multiple body sites on the infant and used whole-genome shotgun sequencing metagenomics, rather than 16S rRNA amplicon sequencing alone, as other studies have done.

Microbiota at Four Body Sites, at Birth and 6 Weeks

Specifically, the team enrolled 81 pregnant mothers who were in their third trimester. The researchers took samples from the mouth, nostrils, skin (inner elbow and behind the ear), stool (representing the gut), and vagina from the mothers, and samples from the mouth, nostrils, skin, and meconium or stool from the neonates at the time of delivery and 4 to 6 weeks later (referred to as 6 weeks).

They also enrolled a matched cross-sectional cohort of 82 mother–neonate pairs that were only sampled at the time of delivery.

In total, the researchers obtained samples from 157 mother–neonate dyads, of which 105 mothers delivered vaginally and 52 delivered by cesarean surgery.

The study controlled for reasons for a cesarean delivery, to separate the delivery from "the company it keeps," or the underlying medical reasons for a cesarean delivery, Dr Aagaard said.

They also chose to take samples at 6 weeks because the infants were being fed by breast milk, formula, or both (which the researchers could control for) and had limited exposure to daycare, vaccines, and antibiotics at that time, she added.

The neonatal microbiota was sparsely populated at the time of delivery, but its scope and function significantly expanded and diversified with demonstrable body site specificity by 6 weeks (P < .001).

Moreover, "each body niche was enriched for taxa that were characteristic of their adult counterparts (such as Streptococcus in the oral cavity), likely indicating a common maturation process," Chu and colleagues report.

However, there were no discernable differences in the bacterial community structure or function in infants born via vaginal delivery or cesarean surgery (P = .057).

"One of the interesting observations in this study is that infants are not sterile," Dr Aagaard pointed out, which is consistent with the growing body of evidence that challenges the concept of a sterile in utero environment.

The group plans to continue this line of research, she said, and "delve into where the neonate microbiome really arises from."

The authors have disclosed no relevant financial relationships.

Nat Med. Published online January 23, 2017. Abstract

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