The findings arrive at a crucial moment. Over two million women of reproductive age in the U.S. live in maternal health care deserts, where there is very limited access to obstetric services. Coinciding with this lack of access, pregnancy problems like miscarriage and preterm delivery continue to represent major dangers to mother and child health, requiring more efficient methods of monitoring and treating these outcomes.
Aligning Heart Rates and Hormones
Researchers used PowerMom, a multilingual digital research platform that allowed participants to share health information from their personal wearables after giving consent. The platform allowed the team to gather information beyond standard prenatal clinic appointments.
The researchers engaged with almost 5,600 volunteers who expressly agreed to disclose their data. 108 volunteers provided continuous data over a three-month period, spanning from before pregnancy to six months postpartum. Advanced statistical methods helped the team identify population-level trends while accounting for individual differences and device types.
Analysis of the shared data revealed that heart rate patterns were linked with hormonal changes, including estrogen, progesterone, and human chorionic gonadotropin (hCG), all essential markers of hormonal progression during and after pregnancy.
A notable pattern from the data was a dip in heart rate between week five and nine, followed by a steady incline and a peak at about eight to nine weeks before delivery, up to 9.4 beats per minute higher than pre-pregnancy levels.
After giving birth, rates fell below baseline values before stabilizing roughly six months later. The researchers also monitored sleep and activity habits throughout the pregnancy.
To verify these findings, the scientists compared wearable sensor patterns to published hormone-level data from prior pregnancy studies, building predictive models that aligned heart rate changes with expected hormonal shifts. While these results are preliminary, they show that wearables may improve prenatal care, particularly for women living in maternal care deserts.
Hormones play a key role in pregnancy outcomes. Discovering the association between heart rate and hormone changes could unlock new ways to predict the beginning of pregnancy or identify signs of adverse outcomes such as gestational diabetes or preeclampsia.
Tolúwalàse Àjàyí, Study Co-Senior Author and Principal Investigator, PowerMom
In a smaller subset of cases, pregnancies that ended in miscarriage or stillbirth showed distinct heart rate patterns compared to healthy pregnancies. The researchers plan to further investigate these findings for a clearer perspective on these results.
The Future of Health Monitoring
This study takes a huge step toward making pregnancy monitoring more accessible using technologies that many people currently possess and use. The technique, which converts consumer products into medical monitoring tools, might help bridge healthcare gaps and offer continuous monitoring for high-risk pregnancies.
The Scripps team now plans to explore how pregnancy-related patterns vary across different populations, ages, and socioeconomic groups to eventually create more personalized care models.
We want to understand if these patterns are consistent across subgroups based on age and access to care. Our goal is to determine whether this approach could eventually contribute to more personalized pregnancy care.
Giulia Milan, Study First Author and Graduate Student, University of California, San Diego
Future studies will combine wearable data with blood samples from the same participants to directly confirm the link between hormones and heart metrics. If validated, the approach could support wider clinical decision-making and improve patient outcomes.
Journal Reference:
Milan, G., et al. (2025) Association between wearable sensor signals and expected hormonal changes in pregnancy. eBioMedicine. doi.org/10.1016/j.ebiom.2025.105888.