Pregnancy comes with its own quirks. A new study suggests that the composition of gut bacteria in pregnant woman is so diverse that it could easily lead to weight gain and inflammation. However, during pregnancy, this diversity in gut microbiota actually benefits the woman.

"This is the first in-depth characterization of the gut microbiota associated with pregnancy. The findings suggest that our bodies have coevolved with the microbiota and may actually be using them as a tool—to help alter the mother's metabolism to support the growth of the fetus," said Ruth Ley from Cornell University and senior author of the study.

Researchers found that during pregnancy, these microbes help in fat storage and help the baby grow. At other times, having these microbes in the body could lead to weight gain and type 2 diabetes.

The present study included approximately 90 pregnant women. Researchers analyzed stool samples of these women and found that the diversity of gut microbes changed dramatically from the first to the third trimester.

They found that disease inducing bacteria increased in number in the third trimester while bacteria that are good for the body had decreased.

The researchers found that signs of inflammation, an indication that the body's immune system is trying to kill the foreign objects in the body, increased from the first to the third trimester

Researchers say that the microbes weren't related to the diet of the mother and that other factors like hormones might be influencing the composition of microbes.

Researchers then tested the effects of these microbes on healthy germ-free mice. They found that compared to mice that received first trimester microbes, mice receiving third trimester microbes were fat and had bad glucose metabolism.

"By the third trimester, the microbiota can induce changes in metabolism. 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," Ley said in a news release.

The study was published in the journal Cell.