Contributed by Megan Holm, M.S. & Sofie Jacobsen, M.S.
New research & what it contributes
Eight Sleep Labs announced findings from a new study (available now via preprint). The study characterizes how sleep temperature preferences (using the Pod), sleep, and cardiovascular recovery (heart rate (HR) and heart rate variability (HRV)) change across pregnancy and postpartum.
The study observed 108 pregnant women from 12 weeks before pregnancy through up to 24 weeks postpartum. To date, it is the most comprehensive study exploring pregnancy changes on a nightly basis and introduces brand new pregnancy and postpartum-period metrics, like sleep temperature preferences, snoring, deep sleep, and REM sleep. It’s also the only study to show that Pod members experience smaller pregnancy-related cardiovascular recovery and sleep changes in addition to more favorable postpartum-period recovery than women who presumably were not sleeping on the Pod (identified in large-cohort wearable studies).
Key takeaways
- Women prefer a cooler bed as pregnancy progresses. On average, women lower their Pod temperature by approximately 2°C (4°F). This varies the most during the third trimester, where settings range from 11.7°C cooler to 3.2°C warmer compared to their pre-pregnancy preferences.
- Women sleeping on the Pod have better sleep and recovery during the third trimester of pregnancy, compared to women not sleeping on the Pod. On average, Pod members have 12 minutes more sleep, including 7 more minutes of deep sleep, 3 bpm lower HR, and 2 ms higher HRV each night.
- The standard postpartum recovery window is six weeks (source), so most research focuses on this period. We followed women for six months (24 weeks) and found that HR and HRV rebound within 12 weeks, but sleep doesn’t return to pre-pregnancy levels during this timeframe.
Women’s sleep temperature cools progressively across pregnancy
Temperature is important for sleep quality, yet how temperature (core body and preferences) changes across pregnancy and postpartum remains poorly studied. To date, only one peer-reviewed study characterized temperature changes across pregnancy.
Researchers in the aforementioned study found a ~0.7°C decrease in core body temperature and reported that a 4°C room-temperature decrease across pregnancy was required to keep body temperature stable. The study reported daytime core temperature and room temperature measurements, but did not report nighttime changes.
We wanted to understand how women’s nighttime temperature preferences change across pregnancy, using Pod temperature as a measure of thermal demand. Similar to core body and room temperature changes, we found that women cool their Pod temperature ~2°C on average across pregnancy (Figure 1 below).
Figure 1. Pod temperature adjustments from 12 weeks before pregnancy start through up to 24 weeks postpartum. Time is shown continuously on the x-axis in weeks and Pod temperature is shown on the y-axis in degrees Celsius (°C). On the x-axis, the dotted line marks the start of pregnancy; the dashed line marks delivery. In the Figure, the three lines represent Pod temperature phases: black line = Bedtime, darker blue line = Night phase, and aqua blue = Dawn phase.
Overnight temperature regulation eases strain during pregnancy and postpartum
We also wanted to better understand how temperature regulation impacts sleep and recovery biometrics across pregnancy and the postpartum period.
Existing literature shows that pregnancy increases demand on the body. HR steadily rises and HRV falls until delivery, indicating that the cardiovascular system is working hard (source). During late pregnancy, deep sleep, REM sleep, and total sleep time (TST) all decrease (source). Right after birth, total sleep time drops even more dramatically due to nighttime caregiving responsibilities (source).
These existing studies leveraged wearable technologies (source, source, source, source) to quantify these changes among large groups of women. Building on this, we asked a new question: Could active temperature regulation via the Pod ease the strain of pregnancy and postpartum?
We found the same trend of cardiovascular and sleep changes among women using the Pod, but the changes are smaller. This suggests that the Pod eases strain during pregnancy and postpartum.
During the postpartum period, we found that on average, cardiovascular metrics (HR, HRV) rebound to better than the pre-pregnancy baseline during the first 12 weeks postpartum, and remain better than baseline even up to 24 weeks after delivery (Figure 2 below).
Figure 2. Weekly HR and HRV from 12 weeks before pregnancy start through up to 24 weeks postpartum. Time is shown continuously on the x-axis in weeks, as gestational age during pregnancy and as weeks since delivery after birth. The top panel shows heart rate on the y-axis in beats per minute (bpm), and the bottom panel shows HRV in milliseconds (ms). In both panels, the dotted line marks the estimated start of pregnancy (last menstrual period, LMP) and the dashed line marks delivery. The dark red line is the weekly mean heart rate, the red line is the weekly mean HRV.
However, core sleep indicators such as total sleep time (TST), nighttime awakenings (wake after sleep onset, WASO), and rapid-eye-movement (REM) sleep do not return to pre-pregnancy levels 24 weeks postpartum. As expected, deep sleep, measured as a percentage of the night, increases as TST falls (Figure 3 below). This is a natural adaptation of the body as it prioritizes physiological recovery during limited periods of sleep (source).
Figure 3. Weekly light, REM and deep sleep from 12 weeks before pregnancy start through up to 24 weeks postpartum. Time is shown continuously on the x-axis in weeks: gestational age (weeks since the estimated last menstrual period, LMP) up to week 40, then weeks since delivery. Each sleep stage is shown on the y-axis as a percentage of total sleep (%). In all three panels, the dotted line marks the estimated start of pregnancy (LMP, gestational week 0), and the dashed line marks delivery, placed right after gestational week 40. From top to bottom, the panels show light sleep (light green line), REM sleep (medium green line) and deep sleep (dark green line).
New and noteworthy
This study is the first to:
- Characterize sleep temperature preferences across pregnancy and the postpartum period.
- Establish the Pod as a potential tool to ease pregnancy and postpartum-period strain.
- Evaluate cardiovascular recovery and sleep stage metrics through 24 weeks into the postpartum period.
Interested in learning more about how Eight Sleep supports sleep during pregnancy? Check out Pregnancy Mode
