Oura’s latest study analyzed data from more than 10,000 pregnancies to chart how temperature, sleep, heart rate and other key metrics evolve from conception through postpartum
A new study from Oura has provided a detailed look at how the human body changes throughout pregnancy, drawing from on collected from the Oura Ring.
Published in JMIR mHealth and UHealth, the research tracked over 10,000 pregnancies to better understand how physiological markers like sleep, heart rate, body temperature and activity shift from conception to recovery after birth.
Here are the key findings that outline how the body adapts but also reveal subtle early variations that could inform future research into pregnancy outcomes.
1. Body Temperature Rises Early & Stays Elevated
Body temperature began increasing around week 4, peaking at roughly +0.3°C by week 9, and remained higher than baseline through most of pregnancy. A smaller secondary rise appeared close to birth. These early, sustained changes highlight how temperature regulation shifts quickly to support pregnancy.
2. Resting Heart Rate Increases While HRV Declines
Resting heart rate rose steadily, reaching about +10 beats per minute by week 32, while heart rate variability (HRV), a measure of nervous system balance, declined by more than 15 milliseconds. This reflects growing cardiovascular demands as pregnancy progresses.
3. Sleep Duration Shifts Over Trimesters
In the first trimester, participants slept slightly longer, about 15 minutes more per night, before sleep duration and quality gradually declined, reaching a low point near delivery. The data provide a quantitative look at how sleep patterns change through each stage of pregnancy.
4. Respiratory Rate Peaks Early
Breathing rate increased early in pregnancy, peaking around week 9, then returned to baseline and dipped slightly below it postpartum. The overall change was small, around one additional breath per minute, but consistent across participants.
5. Physical Activity Gradually Declines
Activity levels and daily step counts declined steadily throughout pregnancy, following a clear downward trend from pre-pregnancy to delivery. The data mirror what many experience anecdotally as physical comfort and energy fluctuate over time.
6. Early Physiological Deviations Tied to Pregnancy Loss
Participants who experienced pregnancy loss before 20 weeks showed subtle but notable early differences, including smaller temperature increases, less sleep and reversals in resting heart rate and respiratory rate trends. These findings aren’t diagnostic but suggest continuous data could help identify atypical patterns earlier in pregnancy.
Establishing a Baseline for Pregnancy Research
The Oura study offers one of the most comprehensive continuous datasets of pregnancy physiology to date, providing a clearer understanding of what healthy adaptation looks like across thousands of pregnancies.
“It may seem surprising, but this research is one of the few papers that even begins to describe what is considered normal for a pregnancy,” said Dr. Chris Curry, Oura’s clinical director of women’s health. “Once we establish and validate what a healthy baseline is, we can start to explore patterns that may be linked to disease risk.”
