Maternal weight may influence microbiota signalling in amniotic fluid

The study analysed stool and amniotic fluid samples from 60 pregnant women. Researchers investigated how maternal factors during pregnancy affect small particles produced by the body’s microbiota, known as extracellular vesicles. These are signalling particles released by bacteria that enable microbes to communicate with one another and influence the host’s cells.

“Microbiota-derived vesicles are likely one of the most important communication mechanisms between the microbes in our bodies and our cells. The fetal environment refers to the conditions surrounding the fetus in the womb, including the amniotic fluid. Microbiota signalling within the fetal environment, and changes in that signalling, may have a significant impact on the development of the fetal immune system, for example,” says Jenni Turunen, Postdoctoral Researcher at the University of Oulu.

The researchers found that the profile of microbiota-derived vesicles in both the gut and amniotic fluid varied between mothers. Maternal overweight, obesity, gestational diabetes and weight gain of more than 15 kilograms during pregnancy were associated with microbiota-derived vesicle profiles, particularly in amniotic fluid. In these mothers, the proportion of vesicles produced by certain bacterial groups was lower than in the other study participants.

Previous studies have identified associations between maternal weight and the composition of the microbiota during pregnancy. In addition, the fetus was long thought to develop in a sterile environment. The newly published study is among the first to examine the interaction between microbiota-derived vesicles and pregnancy-related factors, with a particular focus on the fetal environment.

According to Turunen, microbiota-derived vesicles could offer new opportunities for monitoring health during pregnancy.

“In the future, microbiota-derived vesicles could serve as biomarkers of maternal and fetal health, for example. However, before any clinical applications can be considered, we need a better understanding of the functions of these vesicles in the body. Our research group is already carrying out further studies to investigate these questions,” Turunen says.

The findings have been published in the international journal BMC Medicine: Turunen, J., Kyrö, K., Virta, J. et al. Maternal factors associate with microbiota-derived extracellular vesicle profiles in pregnancy: a clinical cohort study. BMC Med (2026).