Gut Microbes Influence Metabolism During Pregnancy

A new study shows that pregnancy alters microbe populations in the gut. The interactions with these microbes cause metabolic changes that likely help the pregnant mother and developing baby.

Pregnancy causes many changes to a woman's metabolism and immune system, including weight gain, reduced insulin sensitivity and inflammation. These changes are similar to those seen in metabolic syndrome, a group of conditions that increases the risk for type 2 diabetes, heart disease and stroke. Recent research shows that certain changes in microbes within the gut (the gut microbiota) can promote some of the physiological changes associated with metabolic syndrome.

In research funded in part by NIH, a team of scientists led by Dr. Ruth E. Ley of Cornell University explored how pregnancy alters the gut microbiota and how microbes might affect metabolic changes during pregnancy. The scientists obtained stool samples, diet information and clinical data from 91 pregnant women during the first and third trimesters. They analyzed microbial DNA from the stool samples to identify microbes during early and late pregnancy. The study was published on August 3, 2012, in Cell.

The researchers found that the microbiota changed considerably from the first to the third trimesters. The first trimester microbiota was similar among subjects and comparable to that of healthy men and nonpregnant women. By the third trimester, however, microbiota varied substantially more between the women. Microbial richness decreased while levels of certain types of microbes, such as Proteobacteria and Actinobacteria, increased. These changes are similar to what's been seen in a mouse model of metabolic syndrome. The changes occurred regardless of the women's initial body weight or whether they developed gestational diabetes.

Stool samples collected from infants, at 1 month to 4 years of age, showed that the mothers' altered third trimester microbiota wasn't passed on to their children. Regardless of age, the children's microbiota was more similar to their mothers' microbiota during the first trimester.

Although changes in microbe diversity didn't appear to affect the mothers' health, stool collected during the third trimester revealed more signs of inflammation than that collected during the first trimester. To find out if pregnancy-associated microbes were causing this inflammation, the researchers transferred microbes from collected stool samples into mice that contained no microbiota of their own. Mice receiving microbes from the third trimester samples had more inflammation and became fatter and less sensitive to insulin than mice receiving first trimester samples.

“By the third trimester, the microbiota can induce changes in metabolism,” Ley says. “In the context of pregnancy, these metabolic changes in the mother are healthy, because they promote energy storage in fat tissue and help support the fetus. Outside of pregnancy, however, these changes can lead to the development of type 2 diabetes and other health problems.”

The next step will be to find out what's causing changes to the microbiota during pregnancy. These changes weren't associated with diet, health status, previous births or antibiotics. The researchers think that the immune system or hormones might play a role.

—by Miranda Hanson, Ph.D.