The Pregnancy Bug(s)

We are all very familiar with the ways in which invading bacteria can make us sick. Lately, however, the research community has been paying increased attention to the role that our ever-present local bacterial populations play in health and disease.

At any given time, each of us has approximately ten times more bacterial cells than human cells living in and on us; this collection of microbes is known as our microbiota. The specific composition of this microbiota is affected by our behavior and environment and, in turn, influences many aspects of our physiology. While these bacteria are incredibly important for digestion and maintaining gut homeostasis, certain classes of bacteria are associated with pathologies such as obesity, diabetes, and inflammatory bowel disease.

In a new paper in Cell,¹ researchers studied the composition of the gut microbiota in women at various stages of pregnancy.^(a) They found that a particular type of bacteria becomes prevalent specifically in the third trimester and that this coincides with increases in blood glucose and insulin resistance, two hallmarks of metabolic syndrome.^(b) When the researchers transplanted the microbiome of third trimester women into mice, they also began to show signs of insulin resistance and obesity, demonstrating that the bacteria drive the metabolic syndrome. The study’s authors hypothesize that changes in the immune system during the course of pregnancy alter the composition of women’s microbiota, and that this is advantageous because it leads to increased glucose for sustaining the mother and child. If this hypothesis is correct, it would represent a remarkable example of a built-in program for altering the composition of microbiota in order to cope with changing nutrient and energy needs.