By Claire O’Connell
Gut bugs in pregnancy - a curious development
During pregnancy, a woman experiences all sorts of visible changes to her body. Her belly gets larger, she puts down fat deposits and patches of her skin can even change colour. But what’s not so easy to spot are the changes happening inside the gut. And if a new study is anything to go by, those changes can be profound.
It might not be the most appetising of thoughts but, as a human, your gut is typically home to billions of bacteria. The gut ‘microbiome’ has become something of a hot topic in research in recent years, with people asking whether and how the nature of gut bugs could be linked with the body’s immune system, certain diseases and possibly even obesity.
Part of the drive to better understand what the bugs do is to see how the profile of bacteria can change: studies have looked at whether diet, ageing and illness correlate with changes in the makeup of gut bugs. And now a research group with members in the US, Sweden and Finland has been looking at what happens to gut bugs during a woman’s pregnancy too, with some interesting results.
Again it’s not appetising, but they got stool samples from 91 pregnant women in the first and third trimesters of their pregnancies. Then they analysed the bacterial content of the stools and compared them with data from the patients such as body mass index, diet information, other clinical measurements and whether they had developed a condition called gestational diabetes, which can happen in late pregnancy.
And what did they find? In short, the composition and structure of the gut microbial community - the bacteria that hang out in the gut - changed profoundly between the first and last trimesters of pregnancy. “By the third trimester, each woman’s microbiota has diverged in ways that could not be predicted from the [trimester 1] composition and that were not associated with health status or our diet records,” write the authors in the journal Cell.
Overall, the diversity of bacteria within an individual person’s gut seemed to reduce between the start and the home furlong of pregnancy. And if you look at the bacteria that typically lived in the gut of a woman in the last trimester of pregnancy, you could be forgiven for thinking they had come from someone who is not in the peak of good health. In fact they resembled the kind of profile that you might expect from someone with metabolic syndrome, a state of health that pushes up the risk of heart disease and diabetes. Plus the types of bacteria that seemed to come to the fore in the gut in late pregnancy are also linked with inflammatory conditions.
And interestingly, when the researchers transferred the bacteria (pooled from the samples of five healthy-weight women) into mice that had no microbiome of their own, they found the mice who got trimester-3 bugs put on more fat and became less sensitive to the hormone insulin than the mice who got the trimester-1 gut bugs.
So overall the gut bugs in late pregnancy resemble the gut bugs from a diseased state. Yet the woman is simply pregnant. But in the journal paper that describes the work, the study authors point out that context can matter.
“Dysbiosis [microbial imbalance], inﬂammation, and weight gain are features of metabolic syndrome, which increases the risk of type 2 diabetes in nonpregnant individuals,” they write. “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.”
Host Remodeling of the Gut Microbiome and Metabolic Changes during Pregnancy
Omry Koren, Julia K. Goodrich, Tyler C. Cullender, Aymé Spor, Kirsi
Laitinen, Helene Kling Bäckhed, Antonio Gonzalez, Jeffrey J. Werner,
Largus T. Angenent, Rob Knight, Fredrik Bäckhed, Erika Isolauri, Seppo
Salminen, Ruth E. Ley
Cell - 3 August 2012 (Vol. 150, Issue 3, pp. 470-480)