Gut microbiota drive metabolic changes in pregnancy

By Eleanor McDermid, Senior MedWire Reporter

Changes in gut microbiota during pregnancy result in unfavorable metabolic changes that are actually beneficial to a pregnant woman and her developing baby, shows research published in Cell.

The gut microbiota changes that occurred between the first and third trimesters are normally associated with features of the metabolic syndrome, such as inflammation, insulin resistance, and obesity.

"These same changes are central to normal pregnancy, where they may be highly beneficial, as they promote energy storage in fat tissue and provide for the growth of the fetus," say Ruth Ley (Cornell University, Ithaca, New York, USA) and team.

When the researchers transferred gut microbiota from pregnant women into mice, they found that mice given microbiota from women in the third trimester had significantly increased markers of inflammation, compared with those given first-trimester microbiota. They also developed significantly more adiposity, at 49.9% versus 37.9%, despite similar food consumption, and had significantly higher glucose levels and nonsignificantly lower levels of insulin.

Besides demonstrating the unhealthy metabolic effects of third-trimester microbiota, the effects in mice also suggest that the shift in gut microbiota is causing the metabolic changes, rather than the reverse scenario.

During pregnancy, the gut microbiota in 91 pregnant women became progressively less diverse within individual women, although there was increased variation between the women. About two-thirds of the women had increases in Proteobacteria (0.7 to 3.2% of all taxa) and Actinobacteria (5.1 to 9.3%).

The changes observed by the third trimester were unrelated to women's gut microbiota in the first trimester, or to their health or diet during pregnancy.

These changes did not notably affect the babies, whose gut microbiota bore more resemblance to their mothers' first- than third-trimester microbiota. This suggests that many of the taxa that are dominant in the mothers' guts during the third trimester are at a selective disadvantage in the babies guts, say Ley et al.

"The underlying mechanisms resulting in the alteration of the microbiota remain to be clarified, but we speculate that the changes in the immune system at the mucosal surfaces in particular precipitate changes in the microbiota, although hormonal changes may also be important," say the researchers.

They add: "Thus, the origins of host‑microbial interactions that skew host metabolism toward greater insulin resistance, and which underlie much of the present-day obesity epidemic, may lie in reproductive biology."

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