Maternal stress hormone levels during early pregnancy can have a lasting effect on the stress system of the offspring. The results of a long-term study on wild Assamese macaques in Thailand indicate that maternal stress in the first half of pregnancy is particularly relevant. Elevated stress hormones later during pregnancy or after birth did not have the same effects. The long-term study conducted by the University of Göttingen and the German Primate Center — Leibniz Institute for Primate Research provides important insights into the influence of early life stages on the development of the stress system under natural environmental conditions.
Influence of very early life stages
The research team investigated how maternal stress affects the stress hormone system of the offspring. They found that the activation of the hypothalamic-pituitary-adrenal (HPA) axis, which plays a central role in coping with stress, can be significantly influenced by exposure to maternal glucocorticoids during development. The early phase of organ differentiation in the first half of pregnancy proved to be a particularly critical period. “Our results show that the HPA-axis activity of offspring was enhanced, the more adversity the other had experienced during early pregnancy — which could be food shortages or social conflicts for example,” says Simone Anzá, former doctoral student at the University of Göttingen and the German Primate Center and first author of the study.
Investigation in the wild
In contrast to studies in the laboratory, the monkeys were observed in their natural habitat. Over a period of nine years, the researchers repeatedly collected fecal samples from pregnant females and measured the concentration of glucocorticoid metabolites in them in order to determine the animals’ exposure to environmental factors such as food scarcity, temperature fluctuations and social interactions. These values were compared with the stress hormone levels of the offspring at different ages. The effects on the stress axis of the offspring were evident from infancy through the juvenile period and into adulthood at nine to ten years of age. Previous analyses from the same study had already shown that early prenatal stress was also associated with altered growth, negative changes in the gut microbiome and impaired immune function, underlining the comprehensive influence of the environment in the early prenatal period on various physiological systems. In contrast, maternal glucocorticoid levels in late pregnancy or during lactation had no or different influences.
Relevance for health research
“Our research results indicate that the timing of maternal stress hormone exposure during and after pregnancy crucially affects the consequences for the development and health of the offspring. It is also important to note that these effects do not require catastrophic events, but that even moderate changes in environmental conditions are sufficient,” says Oliver Schülke, scientist at the University of Göttingen and the German Primate Center and head of the study. Stress in early pregnancy can also have a long-term effect on health in humans and increase the risk of stress disorders and immune problems. “Our findings may help to identify the timing and mechanisms that preventive measures should address in order to reduce long-term health risks,” says Oliver Schülke.
