Pregnancy and weight gain: the role of the intestinal microbiota


A Finnish study provides new information regarding the role of intestinal microbiota during pregnancy and its involvement in increased body mass in pregnant women.


Pregnancy is a period of great hormonal, metabolic and immunological upheaval. The intestinal microbiota is no exception: it is now known to be affected by maternal obesity and to impact the health of both the mother and the unborn child. A team of researchers investigated if it was also linked to weight gain by the expecting mothers.

Two dominant bacterial populations

Analysis of the microbiotas at 24 weeks of pregnancy unsurprisingly showed dominance of bacteria from the Firmicutes phylum (53.3% of women) and the Bacteroidetes phylum (45.9 %), two phyla which contain most of the bacteria that make up the intestinal flora in humans. The researchers then divided the cohort into two groups according to whether Firmicutes or Bacteroidetes were dominant (28 individuals versus 18) in order to correlate these data with clinical characteristics.

Weight gain: which bacteria are predominant?

The researchers showed that weight gain in mothers during pregnancy was greater in the group in which Bacteroidetes was predominant, while 61% of this group had a normal starting weight. Simultaneously, 85.7% of women in the Firmicutes group, which was larger, had a normal weight before their pregnancy. However, no correlation could be established between BMI before pregnancy and the composition of the microbiota.

Decreased bacterial diversity

Another key subject was the reduction in bacterial diversity observed in Bacteroidetes-dominant mothers. This observation suggests that a healthy intestinal ecosystem is correlated with a high level of microbial diversity, unlike in inflammatory intestinal pathologies or obesity for example. This study supports the hypothesis of a link between the composition of the gastrointestinal microbiota and weight gain during pregnancy. Notwithstanding, additional studies will need to be performed in larger cohorts of pregnant women, taking into account food intake, among other things, in order to better understand this relationship.



Aatsinki, A.-K. et al. Gut Microbiota Composition in Mid-Pregnancy Is Associated with Gestational Weight Gain but Not Prepregnancy Body Mass Index. J Womens Health (Larchmt) (2018). doi:10.1089/jwh.2017.6488