Pregnancy triggers a radical shift in human gut microflora, moving the body towards a diabetes-like condition.

Ruth Ley at Cornell University in Ithaca, New York, and her team analysed the faecal bacteria of 91 pregnant women. During the first trimester, these women's bacterial populations were similar to each other and to those of non-pregnant women. But by the third trimester, there were marked differences between the mothers-to-be, and their average gut make-up resembled that seen in a mouse model of metabolic syndrome — a collection of symptoms linked to diabetes.

When the microbiota from third-trimester women were transferred into mice, the animals gained more fat and became less sensitive to insulin than did mice that received first-trimester microbes. Mammals can manipulate their gut biology to trigger changes beneficial to a developing fetus, the researchers suggest.

Cell 150, 470–480 (2012)