In a new study in Cell, researchers from Cornell University show how a woman's gut microbiome can change over the course of a pregnancy, says Not Exactly Rocket Science's Ed Yong. What the study shows is not only how much the composition of the microbiome changes in those nine months, but also how much a healthy microbiome can come to resemble that of a person with a metabolic disorder like obesity or high blood sugar, Yong says. "It's a good reminder that context matters. These 'unhealthy' changes in our gut microbes are actually normal in a different setting, and might even be necessary for a healthy pregnancy," he adds. By collecting stool samples from 91 pregnant women and sequencing their microbes, the researchers found that the women — who started out with healthy guts — lost much of their microbial diversity as they approached the third trimester. And when the researchers transplanted gut bacteria from the pregnant women into mice, the mice quickly developed metabolic problems and put on more weight than the mice transplanted with first-trimester microbes, Yong says.
What the study also shows is that researchers hoping to use the state of a person's gut microbiome to diagnose disease or predict risk have their work cut out for them. "If such readouts can't yet distinguish between someone in poor health, and someone with child, they clearly still have a long way to go," Yong adds.