Monitoring One Heart to Help Two: Heart Rate Variability and Resting Heart Rate using Wearable Technology in Active Women Across the Perinatal Period

Abstract

BACKGROUNDCharacterizing normal heart rate variability (HRV) and resting heart rate (RHR) in healthy women over the course of a pregnancy allows for further investigation into disease states, as pregnancy is the ideal time period for these explorations due to known decreases in cardiovascular health. To our knowledge, this is the first study to continuously monitor HRV and RHR using wearable technology in healthy pregnant women.METHODSA total of eighteen healthy women participated in a prospective cohort study of HRV and RHR while wearing a WHOOP® strap prior to conception, throughout pregnancy, and into postpartum. The study lasted from March 2019 to July 2021; data were analyzed using linear mixed models with splines for non-linear trends.RESULTSEighteen women were followed for an average of 405.8 days (SD=153). Minutes of logged daily activity decreased from 28 minutes pre-pregnancy to 14 minutes by third trimester. A steady decrease in daily HRV and increase in daily RHR were generally seen during pregnancy (HRV Est. = -0.10, P<0.0001; RHR Est. = 0.05, P<0.0001). The effect was moderated by activity minutes for both HRV and RHR. However, at 49 days prior to birth there was a reversal of these indices with a steady increase in daily HRV (Est.=0.38, P< 0.0001) and decrease in daily RHR (Est. = -0.23, P< 0.0001), regardless of activity level, that continued into the postpartum period.CONCLUSIONSIn healthy women, there were significant changes to HRV and RHR throughout pregnancy, including a rapid improvement in cardiovascular health prior to birth that was not otherwise known. Physical activity minutes of any type moderated the known negative consequences of pregnancy on cardiovascular health. By establishing normal changes using daily data, future research can now evaluate disease states as well as physical activity interventions during pregnancy and their impact on cardiovascular fitness.

Wearable-Derived Maternal Heart Rate Variability As A Novel Digital Biomarker of Preterm Birth

“…Our sample size is larger than previous studies and especially with the continuous data points, allows for meaningful conclusions to be drawn. Additionally, we reproduced the results of the prospective study conducted by Rowan et al (2022) with women recruited from a single site fertility clinic in West Virginia experiencing singleton pregnancies. Our study represents women from 42 US states and territories and 16 countries.…”

“…To explore the inflection point of HRV in pregnancy, for each population we fit two mixed-effect spline models to the average weekly HRV within-subject by gestational age and by weeks from birth. A spline model was selected due to the nonlinear nature of HRV during the third trimester of pregnancy (Rowan et al, 2022). A mixed-effect model was selected due to the natural variations of HRV from subject to subject.…”

“…Model 1 utilized average weekly HRVs as the response variable and gestational week starting from week 24 until the reported date of birth as the explanatory variable in a linear spline model to assess if gestational age explains changes in HRV. Based on the findings by Rowan et al, 2022, that the declining trend in HRV reverses at 33 weeks gestational age, a linear spline model with a knot at 33 gestational weeks was fit for each group and evaluated for significance and fit. Model 2 utilized average weekly HRVs as the response variable and weeks until birth from the actual date of birth backward until week 24 as the explanatory variable in a linear spline model to assess if time until birth explains changes in HRV.…”

“…Model 2 utilized average weekly HRVs as the response variable and weeks until birth from the actual date of birth backward until week 24 as the explanatory variable in a linear spline model to assess if time until birth explains changes in HRV. Based on the findings by Rowan et al, 2022, that the trend in RHR and HRV reverses 7 weeks prior to delivery, a linear spline model with a knot 7 weeks from birth was fit to each group and evaluated for significance and fit.…”

“…The WHOOP Strap (Whoop, Inc., Boston, MA, USA) is a commercially available wearable device that provides continuous physiological data including HRV for a range of applications, including predicting COVID-19 (Miller et al, 2020) and risk of adverse mental health outcomes (Czeisler et al, 2022)). Rowan et al (2022) utilized the WHOOP Strap to describe decreases in maternal HRV during term pregnancies until approximately 33 weeks when the trend reversed and increased through delivery. All pregnancies in that study were delivered at term, leaving the cardiovascular trends that occur throughout pregnancy in preterm births unexamined.…”