We have all felt it – stress. Sometimes it is a powerful ally that helps us perform better in an exam or when giving a talk. But when it turns into a long-lasting partner, it can become a serious health problem that may even interfere with our ability to live a normal life. Furthermore, stress is a key issue in certain periods of our life, such as pregnancy.

A number of scientific studies have already linked stress in pregnant women to premature birth, low birth weight, some skin conditions, asthma and even anxiety and attention-deficit hyperactivity disorder (ADHD). However, the reasons underlying these associations remain elusive. So what if gut microbiota played a role?

A new study by researchers from the Behavioural Science Institute of Radboud University Nijmegen in the Netherlands, published in the journal Psychoneuroendocrinology, appears to shed some light on this link between stress in pregnant women and their babies’ microbiota.

According to the authors of the study, mums who experience high and prolonged levels of stress during gestation are more likely to have infants with more probabilities of suffering intestinal problems and allergic reactions.

The scientists recruited 56 pregnant mothers and measured women’s levels of stress by asking them to complete a questionnaire and to provide a saliva sample in which they analysed the concentrations of cortisol (the so-called stress hormone) prior to delivery. The Dutch researchers subsequently examined the microbiota of the babies’ guts through stool samples collected from the age of 7 days up until 4 months after birth.

According to this team of experts, there is a correlation between highly stressed pregnant mothers and the composition of microbes in the newborns’ guts. These infants had a significantly higher relative abundance of Proteobacterial groups, known, in the authors’ words, to contain pathogens (Escherichia, Serratia and Enterobacter), and lower quantities of lactic acid bacteria such as Lactobacillus, Lactococcus, Aerococcus and Bifidobacteria.

Altogether, experts consider this pattern to be related to a potentially increased level of inflammation. This aberrant colonization pattern was related to more maternally reported infant gastrointestinal symptoms and allergic reactions. They also saw that breastfeeding, which is known to promote the development of beneficial microbes in the intestine due to the prebiotic content of breast milk, was not enough to protect the baby from the negative effects of its mother’s stress.

Although it remains a theory, researchers speculate that the cortisol may be interfering with bile production, which could, in turn, influence gut bacteria. They also highlight this stress hormone may be able to pass through the placenta and increase cortisol levels in the foetus, thus affecting the development of the gastrointestinal tract.

According to the authors of the paper, the study has shown clear links between the mother’s stress during pregnancy and the baby’s gut microbiota development and health. For these Dutch experts, the results suggest there is a possible mechanism by which maternal prenatal stress influences the development of the foetus. Nevertheless, the reasons behind this link are still unknown and require further research. Finally, researchers from Radboud University Nijmegen consider their findings may open up a potential way for bacterial interventions to improve health and development in babies born to stressed mothers.