Gestation is accompanied by alterations in the microbial repertoire; however, the
mechanisms driving these changes are unknown. Here, we demonstrate a dramatic shift in
the gut microbial composition of women and mice during late pregnancy, including an
increase in the relative abundance of Bifidobacterium. Using in-vivo-transplanted pellets, we
found that progesterone, the principal gestation hormone, affects the microbial community.
The effect of progesterone on the richness of several bacteria species, including …