Pregnancy Study Shows Benefits of Exercise, Useful Trends in HRV & RHR

Results found increased activity led to improved HRV and resting heart rate, plus how monitoring these metrics could help better understand pregnancy timelines.

In 2021 we announced a study from West Virginia University School of Medicine using WHOOP to monitor health trends of active pregnant women. It is the first of its kind to track key biometrics with a wearable device throughout the participants’ entire pregnancy journey–before, during, and afterwards. More than three years in the making, we are now pleased to share the results, which have been published in the scientific journal BioMed Central.  

HRV & Resting Heart Rate Trends in Active Pregnant Women

The goal of the study was to use continuous monitoring of heart rate variability (HRV) and resting heart rate (RHR) to define changes in normal pregnancies of physically active women, as well as to learn if increased levels of activity positively impacted these HR metrics. In total, 38 women were enrolled in the study from March of 2019 until August 2020. They were each between 18 and 35 years old, and all exercising at least 3 times per week with the intention to continue doing so during pregnancy and afterwards. None were pregnant at the time, but all stated that they were hoping to be within the next 6 months. From March of 2019 through June of 2021, WHOOP data was collected for 18 women from conception through delivery, for an average of 406 days. The women were all generally healthy over the course of their pregnancies, and each gave birth after 37-41 weeks.  

Changes In HRV & RHR Prior to First Missed Period

Almost immediately from the time of conception, the participants began to show a decrease in their heart rate variability and an increase in their resting heart rates. In the graphics below, you can see a significant dip in average HRV and bump in average RHR that culminate around the women’s first missed periods at 35 weeks prior to birth. Key Takeaway 1: Monitoring HRV and RHR daily for similar trends could be helpful in detecting pregnancy before the more traditional indicator of a late period.

HRV & RHR Trends Flip 7 Weeks Before Birth

As displayed above, the trends in HRV (down) and RHR (up) continued through most of pregnancy. However, 7 weeks before childbirth they reversed, with HRV beginning to rise and RHR starting to fall. This was a phenomenon never before detected by previous studies. With such a notable change happening in both metrics at this very specific point in the third trimester, it has the potential to be a useful barometer of how much time is remaining in the pregnancy. Key Takeaway 2: This finding could enable physicians to watch out for these shifts in HRV and RHR trends, and in turn possibly take action if they happen sooner than expected.  

It’s Good for You to Get Exercise While Pregnant

Overall, the participants’ average minutes of logged daily activity did decrease during pregnancy, from about 28 minutes pre-pregnancy to 14 minutes by the third trimester. But, the women who were able to be more active had consistently improved HRV and RHR compared to those who were less active. This was particularly true in the first two trimesters of pregnancy and immediately following childbirth. From Dr. Shon Rowan, lead researcher on the study: “Qualitative evidence suggests strong cultural expectations that women should ‘sit down and slow down’ during pregnancy. The guidelines for pregnant women around exercise have changed, but not in a wide-scale or well-known way. Contrary to past recommendations, this study found that any type of activity during pregnancy is beneficial. This isn’t necessarily driven by intensity, but duration.” Key Takeaway 3: Regular exercise has a positive impact on cardiovascular health during pregnancy. Additionally, women can actually make fitness gains while pregnant, as noted by improved HRV metrics after pregnancy compared to beforehand.  

Future Research

“There is a major knowledge and education gap when it comes to studying women’s health,” added Dr. Rowan. “When notable findings like this come through it opens the door for more opportunities to conduct studies driven by wearable technology that consumers have access to, and in turn drive more research that can change guidelines and ultimately contribute to the greater health of the population.” LISTEN NOW: Podcast 165 - Dr. Shon Rowan on Pregnancy Exercise & HRV Study READ MORE: How Pregnancy Impacts Resting Heart Rate, HRV & More