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A groundbreaking study conducted by researchers at Michigan State University and the University of Michigan has provided new insights into the timing of prenatal stress and its effects on infant stress reactivity and temperament. The study, published in Psychoneuroendocrinology, is the first to examine weekly stress across 27 weeks of pregnancy, pinpointing specific periods when prenatal stress most significantly affects a newborn’s biobehavioral responses.
Key Findings and Gender Differences
While prenatal stress has long been linked to negative health outcomes, including mental health issues in children and adults, previous research primarily suggested that girls were more affected. However, the new study challenges this notion, emphasizing that while the effects are not necessarily stronger in one gender, they occur at different times.
“Prenatal stress has a well-established link to negative health outcomes, but most studies conclude that the biggest effects are on girls. Our study found that not to be the case. It’s in fact, just different timing,” said lead investigator Alytia Levendosky, a professor in MSU’s Department of Psychology.
Study Methodology
The study recruited 396 pregnant women, focusing on those from high stress-risk populations due to factors such as low income and exposure to intimate partner violence. Weekly stress assessments were conducted via email or text from week 15 through week 41 of pregnancy.
To assess the effects of stress on infants, researchers collected cortisol levels from the babies at six months postpartum, both before and after a mildly stressful laboratory task. Additionally, mothers provided reports on their infants’ temperament.
Timing of Stress Sensitivity
The results revealed that both mid and late gestation are critical periods for stress sensitivity, but the effects vary by gender. Stress during mid-gestation was found to influence the HPA (hypothalamic-pituitary-adrenal) axis and temperament in girls, whereas late-gestation stress had a greater impact on boys. Previous studies had typically stopped their stress assessments between 32 and 34 weeks of pregnancy. However, this study extended through week 41, allowing researchers to identify the most sensitive period for boys.
“This study is an essential step in correcting our understanding around prenatal stress effects for boys and girls,” said co-investigator Joseph Lonstein, a professor in MSU’s Department of Psychology. “We hope our findings inspire additional research to better understand fetal brain development across pregnancy and how it is affected by stress.”
Future Research Directions
The research team plans to continue tracking these participants until they reach the age of four, with follow-up assessments scheduled at 2.5 and 4 years old. Co-author Amy Nuttall, an associate professor in MSU’s Department of Human Development and Family Studies, hopes to extend the study further into childhood to gain a more comprehensive understanding of the long-term impacts of prenatal stress.
Reference
More information: Alytia A. Levendosky et al., Pinpointing the Timing of Prenatal Stress Associated with Infant Biobehavioral Reactivity, Psychoneuroendocrinology (2025). DOI: 10.1016/j.psyneuen.2025.107368
Disclaimer: This article summarizes findings from a scientific study and should not be used as a substitute for professional medical advice. If you have concerns about prenatal stress or its effects, consult a healthcare professional for guidance.
