Study Shows the Effects of Prenatal Stress Over 27 Weeks of Gestation

A team of researchers from Michigan State University and the University of Michigan has gained new insights into the timing of prenatal stress and its effects on infant stress reactivity and temperament, including gender differences. Published in the journal Psychoneuroendocrinology, the study is the first to examine weekly stress over 27 weeks of pregnancy to determine when it has the greatest impact on the stress response and temperament of the newborn – two measures that indicate the child’s biobehavioral reactivity.

“Prenatal stress has been shown to be associated with negative health outcomes, including mental health, in children and adults, but most studies conclude that the greatest effects are seen in girls. Our study found that this is not the case. It is, in fact, just a different timing,” said Alytia Levendosky, head of the study and professor in the Department of Psychology at MSU.

How Maternal Stress Affects Boys and Girls

The researchers recruited 396 pregnant women who were at high risk of stress due to their low income and/or intimate partner violence. Weekly stress assessments were conducted by email or text message from 15 to 41 weeks of pregnancy. Six months after birth, the infant’s cortisol levels were measured before and after a mildly stressful laboratory task to see how the hypothalamic-pituitary-adrenal (HPA) axis responded to stress. The mothers also reported on their child’s temperament.

The study found that there are periods of heightened sensitivity to stress both mid- and late-pregnancy, but that girls and boys are sensitive to it differently. The data showed that stress in mid-pregnancy affected the HPA axis and temperament of girls, while stress in late pregnancy affected boys. In previous studies in this area, the last stress assessment was set between 32 and 34 weeks. Because this study ran until 41 weeks, Levendosky and her team were able to pinpoint the most sensitive time for boys. “This study is an important step in correcting our understanding of the effects of prenatal stress on both boys and girls,” said Joseph Lonstein, study director and professor in the MSU Department of Psychology.

The researchers hope that their findings will inspire further research to better understand what happens in fetal brain development during pregnancy and how it is affected by stress. Current funding allows the research team to continue monitoring these participants until they are four years old, with assessments at 2.5 years and again at 4 years. Amy Nuttall, co-author of this study and associate professor in the Department of Human Development and Family Studies at MSU, hopes to continue the study into later childhood.

Prenatal Stress is Associated With Gut Microbes in Infants

Previous research from the University of Turku, Finland suggests that chronic prenatal maternal psychological stress and increased cortisol concentrations in hair are associated with the composition of the infant’s gut microbiota. The results of the study help to provide a better understanding of how prenatal stress can be linked to the growth and development of infants. “We were able to show that chronic psychological stress in the mother and increased cortisol concentrations in the hair during pregnancy are associated with the composition of the child’s intestinal microbiota, but not with its diversity,” explains doctoral student Dr. Anna Aatsinki.

The study used hair cortisol analysis, which made it possible to measure the average concentration of the stress hormone cortisol over several months. In addition, the mother’s symptoms during pregnancy were examined three times. The infant’s gut flora was analyzed using next-generation sequencing at 2.5 months of age. Previously, similar studies had focused on animals and two had been small-scale human studies, so these data, from 399 mothers and their infants, are the largest to date worldwide. The results provide significant new information on this phenomenon. In addition, this study was able to confirm previous observations.

Investigating the Role of Microbes as Stress Mediators

Both Proteobacteria and Lactobacillus are common gut microbes in infants. For example, the researchers found that chronic prenatal maternal psychological stress was associated with increased abundance of Proteobacteria genera in infant microbiota. Furthermore, chronic psychological symptoms were associated with a decreased abundance of Akkermansia genera, which are considered to be beneficial, at least in adults.

According to Aatsinki, it was also interesting that low cortisol concentrations were associated with increased abundance of Lactobacillus in the gut microbiota of infants. Lactobacillus bacteria are considered beneficial for health. However, Proteobacteria also include species that can cause inflammation in the body. Furthermore, they may be related to the child’s risk of disease later in life. Therefore, the researchers consider it important to investigate how the observed changes are related to the child’s later development. The study does not explain the cause and effect link or whether prenatal mental stress is related to differences in microbial metabolites or, for example, in the functioning of the immune system. In other words, there are still important questions to be answered.