Pregnant individuals are particularly susceptible to heat stress, but it’s not just about the outside temperature and humidity. Housing quality, cooling effectiveness, energy affordability, and adaptive behaviors also play important roles, according to research by Jazmin Ramirez, B.S.N., RN. She defended her Ph.D. dissertation, titled “Extreme Heat Exposure and Pregnancy: Integrating Biological Mechanisms, Hyperlocal Heat Assessment, and Heat Adaptive Behaviors,” on June 25 at the University of Miami School of Nursing and Health Studies.
“My findings show that heat vulnerability during pregnancy is more complex than environmental temperature alone,” Ramirez explained. “It is also shaped by the biological, behavioral and social factors that influence a person’s ability to adapt.”
Ramirez studied pregnancy heat vulnerability for her doctoral research in the SONHS Ph.D. in Nursing Science program; she successfully defended her dissertation in June. The National Institutes of Health’s (NIH) National Institute of Nursing Research funded her work through a 2.5-year grant (the F31 Ruth L. Kirschstein Predoctoral Individual National Research Service Award).
Interplay of factors drives heat vulnerability
Research has established that physiological changes affecting pregnant individuals’ thermoregulation, cardiovascular function, and hydration make them more vulnerable to heat stress. But gaps remain in understanding how biologic mechanisms, environmental exposures, and adaptive responses all contribute to heat vulnerability during pregnancy.
Ramirez, who spent five years as a neonatal intensive care unit (NICU) nurse before starting the Ph.D. program, wanted to study how these factors might interact in real-time for pregnant women. She studied pregnant individuals in 10 different neighborhoods around Miami-Dade County, gathering data from temperature and humidity sensors placed outdoors in their neighborhoods.
Ultimately, Ramirez conducted three complementary studies:
- A systematic review of evidence on heat stress and placental function,
- An evaluation of how pregnant individuals adapt to the heat and the role of social determinants of health in the ability to adapt, and
- A study on hyperlocal heat exposure and gestational age.
Her review synthesized strong evidence for a relationship between heat stress and placenta, including changes in placental weight, efficiency, blood flow, and gene expression. This supports the placenta as one pathway linking heat to adverse pregnancy outcomes.
In the study of heat adaptations, Ramirez found that most pregnant individuals attempted to adapt to the heat. However, financial and structural barriers limited some participants’ ability to keep cool.
The study on heat exposure and gestational age found no significant association between cumulative heat exposure and gestational weight. “A modest positive association found between third-trimester heat exposure and gestational age only underscores the complexity of pregnancy heat vulnerability,” said Ramirez, a new mother herself during the program.
Taken together, she said, her findings demonstrate that the effects of heat on a pregnant individual are shaped by a combination of social determinants of health, adaptive behavior, biologic susceptibility, and environmental exposure. “Understanding these interactions is essential for protecting maternal and infant health in a changing climate,” she said. “I hope this work helps move the conversation beyond simply measuring temperature and toward developing holistic strategies to protect maternal and fetal health as our climate continues to warm.”
Ramirez’s dissertation committee chair and mentor is the school’s dean, Dr. Hudson Santos, who oversees the NIH-funded Miami-ECHO: A Diverse Cohort of Mothers, Children and Fathers in Miami-Dade County. Her other dissertation committee members were Dr. JoNell Efantis Potter, Miller School of Medicine Department of Obstetrics, Gynecology and Reproductive Sciences; Dr. Raymond Balise, Miller School of Medicine Department of Public Health Sciences; and Dr. Katharine Mach, chair of the Rosenstiel School of Marine, Atmospheric, & Earth Science Department of Environmental Science and Policy.
“Please join us in congratulating Dr. Jazmin Ramirez on successfully defending her dissertation,” announced Dr. Victoria Behar-Zusman, the Ph.D. program director. “This achievement reflects Dr. Ramirez’s dedication, perseverance, and hard work. We are proud of her accomplishment and look forward to her future contributions.”
After graduation, Ramirez said she will begin work as a nurse-scientist, with plans to continue studying maternal and population health.
For more information, visit sonhs.miami.edu/academics/doctoral-programs/phd.
