Study: Bacteria Do Not Colonize Gut Before Birth


The body’s relationship with gut bacteria emerges after birth and in early infancy, during important immunological and physiological development.

New research has found that bacteria essential to digestion and overall health do not begin colonizing the gut until during and after birth, according to a study from investigators at McMaster University.

The study authors examined meconium samples collected from 20 infants during breech Cesarean delivery. Earlier research has sparked controversy by suggesting that humans are colonized by gut bacteria prior to birth, according to the current study. Investigator Katherine Kennedy, a PhD candidate at McMaster University, said these studies have been criticized for the ways they control for contamination. The new research, however, accounted for these concerns.

“By including only breech caesarean deliveries in healthy pregnant women, we were able to avoid the transmission of bacteria that occurs naturally during a vaginal birth,” said co-senior author Thorsten Braun, lead obstetric consultant and deputy director of the Department of Experimental Obstetrics at Charite-Universitatsmedizin Berlin, in the press release.

Contrary to the earlier study findings, the research team found that the gut is not colonized before birth. Instead, Kennedy said the body’s relationship with gut bacteria emerges after birth and during infancy. This relationship is essential in early life, during immunological and physiological development.

“The fact that colonization of infants’ gut occurs during and after their births means that not only is it vulnerable to early environmental influences, but could also offer a window of potential intervention,” said researcher Deborah Sloboda, MSc, PhD, in the press release. “While many of the exact mechanisms surrounding gut bacteria and their role in our early development is unclear, discovering when and how we are colonized is a key first step.”


McMaster University. Bacteria do not colonize the gut before birth, says collaborative study. News release. May 10, 2021. Accessed May 19, 2021.

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