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Not Sterile, After All: The Placenta’s Microbiome

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Pregnant woman smiling and pointing to her tummy

Credit: Chad Cohen

When thinking about your health, or the health of your children, you’re probably not thinking of the placenta. This often neglected, yet vital, pancake-shaped organ develops during pregnancy. It adheres to the inside surface of the uterus and guides development; partly maternal, partly fetal, it delivers food and oxygen to the growing fetus via the umbilical cord and removes waste products—among other vital functions. Yet, the placenta may be even more important to the health of mother and child than we’ve previously imagined.

Until recently, the uterus and the placenta were thought to be germ-free and sterile—to keep the baby safe from infection. But at just one week old, babies have a complex collection of microbes in their guts. Where do those bacteria come from? It was thought that a baby received its first dose of bacteria as it passed through the vagina—or from the mother’s skin, if the child was born via C-section. But Kjersti Aagaard, a 2007 recipient of a NIH Director’s New Innovator Award and an obstetrician and associate professor of gynecology at Baylor and the Texas Children’s Hospital, began to suspect there was more to the story.