Scientists have recently explored the developing fetus and their microbiomes. Previously, doctors considered the womb sterile: the amniotic sac, and the fluid surrounding the baby, was a distinctively clean environment lacking bacteria or other microbial agents to defend the baby and the still developing immune system. Vaginal birth was considered the baby’s first exposure to bacteria, which continues after birth through skin-to-skin contact with mom and from its new environment.

However, current research supports the idea that the baby’s microbiome actually gets established much sooner than previously thought—in the womb. Scientists have detected small populations of bacteria in the amniotic fluid, placenta, and the fetus’ intestines.

Researchers aren’t exactly sure how this happens, but hypothesize that bacteria from the mother’s mouth might travel through the blood stream and reach the developing baby in utero through the placenta. Some bacteria might also travel from the vagina into the womb.

What exactly does this mean? Ultimately, the mother’s health and her microbes might have far greater influence on the baby’s health and development, including vulnerability to disease, than we previously thought. One researcher thinks it might indicate that establishment of the baby’s microbiome begins in utero and can be influenced by the health and diet of the mother during pregnancy. Other studies have found that overweight mothers have different types of bacteria in their gut than those of normal weight mothers, and an expectant mom’s dental health could also have an effect on her baby’s microbiome and later health.

The researchers have stressed it is still early to know the “right” microbiome that’s conducive to a healthy baby, or a “wrong” one that might lead to disease. However, there are certainly things like maternal dental hygiene and not taking unnecessary antibiotics that should be considered. We knew it was important to be healthy during pregnancy, but now, the research indicates how important the mother’s microbiome is.


Park, Alice. "Baby Biomes: Babies in the Womb Aren't So Sterile After All." Time. December 28, 2015.