A groundbreaking study led by researchers at Michigan State University (MSU) and the University of Michigan offers new insights into the timing of prenatal stress and its impact on infant stress reactivity and temperament. Published in Psychoneuroendocrinology, this research is the first to explore the weekly variation in stress levels throughout 27 weeks of pregnancy to identify when prenatal stress most influences a newborn’s stress response and temperament.
Prenatal stress has long been associated with negative health outcomes, including mental health challenges, for both children and adults. While many previous studies have suggested that these effects are more pronounced in girls, the MSU study challenges this conclusion. “Our study found that the timing of stress, not gender, plays a critical role in determining how stress affects the infant,” said Alytia Levendosky, the lead investigator of the study and a professor in MSU’s Department of Psychology.
The study recruited 396 pregnant women from high-risk populations, specifically those exposed to low income and intimate partner violence. Stress assessments were conducted weekly from the 15th to the 41st week of pregnancy, using email and text-based surveys. At six months postpartum, infant cortisol levels were measured before and after a mildly stressful laboratory task to evaluate the hypothalamic-pituitary-adrenal (HPA) axis, which is a key biological system that regulates stress. Additionally, mothers provided reports on their infant’s temperament.
The research found that there were specific periods during pregnancy when stress had heightened sensitivity, particularly in mid and late gestation. However, the effects of stress varied between genders. The data revealed that stress experienced during mid-gestation primarily affected girls, particularly their HPA axis and temperament. On the other hand, stress in the later stages of pregnancy, particularly in the final weeks, had more significant effects on boys. Previous studies in this area typically concluded stress assessments by week 32-34, but this study extended until week 41, allowing the researchers to pinpoint the critical timing for boys.
“This study is a pivotal step in refining our understanding of prenatal stress and its impact on both boys and girls,” said Joseph Lonstein, an investigator on the study and professor in MSU’s Department of Psychology. “We hope that our findings will spark further research, allowing us to gain a deeper understanding of fetal brain development and the specific ways stress affects it throughout pregnancy.”
The researchers are continuing to follow these participants through the age of four, with assessments planned at 2.5 years and again at 4 years old. Co-author Amy Nuttall, an associate professor in the Department of Human Development and Family Studies at MSU, hopes to extend the study into later childhood to further explore the long-term effects of prenatal stress on development.
This research not only challenges existing assumptions but also lays the foundation for more precise interventions in maternal health care, aimed at reducing prenatal stress and its impact on infant development.
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