Why is this study important?

Some people develop dangerously high blood pressure during pregnancy, a group of conditions known as hypertensive disorders of pregnancy. When left unmanaged, these conditions can lead to serious complications for both mother and baby and increase lifetime risk of cardiovascular disease. Hypertensive disorders of pregnancy affect roughly one in seven pregnancies, making them a major public health challenge (1).

Moderate-to-vigorous physical activity during pregnancy reduces the risk of developing hypertensive disorders of pregnancy, yet in the United States fewer than 25% of pregnant people meet the minimum recommendation of 150 minutes per week (2, 3). Levels are similarly low in other regions of the world (4). Given pregnancy-specific barriers to moderate-to-vigorous physical activity, such as fatigue and nausea, it is critical to identify alternative behaviours that may be more feasible intervention targets to improve pregnancy health. Prior to this study, little was known about the health effects of lower-intensity behaviours including sitting, light activity, and sleep on cardiovascular health in pregnancy (5).

How did the study go about this?

To address this gap, the Pregnancy 24/7 cohort study recruited 500 participants across three US sites (Iowa, Pittsburgh, and West Virginia) between 2021 and 2024 (6).. In each trimester, participants wore two devices (activPAL and Actiwatch Spectrum Plus) for seven full days to objectively measure waking movement and time in bed, rather than relying on recall or self-report. The activPAL is a small device worn on the thigh, under clothing, that detects body position and movement to record how much time is spent sitting, standing, and walking. The Actiwatch is worn on the wrist like a watch and estimates sleep and wake patterns from wrist movement and light exposure. Hypertensive disorders of pregnancy were extracted from medical records and confirmed by physicians. For the analysis, we used a technique that combines all 24-hour movement behaviours to identify the optimal daily pattern, paired with a framework known as the “Goldilocks Day” (not too much, not too little) to find a unified recommendation associated with the lowest risk of hypertensive disorders of pregnancy.

What did the study find?

Among the 470 participants with complete data, 18% developed a hypertensive disorder during pregnancy. The most important finding was that the relative time spent in sedentary behaviour or light-intensity physical activity was the strongest and most consistent predictor of developing a hypertensive disorder of pregnancy across all three trimesters.

A realistic and achievable “Goldilocks Day” profile for most pregnant people involved approximately 8 hours per day of sedentary behaviour, 7 hours per day of light-intensity physical activity, 22 minutes per day of moderate-to-vigorous physical activity, and 9 hours per day of sleep. This composition was associated with a 29% reduction in the risk of hypertensive disorders of pregnancy compared with a typical day (around 10 hours sedentary and 5 hours of light activity) and a 68% reduction compared with the worst-case scenario (around 14 hours sedentary and 1.5 hours of light activity).

When we held moderate-to-vigorous physical activity and sleep constant at their typical levels and examined only the trade-off between sedentary behaviour and light activity, risk followed a clear exponential pattern. For example, each additional hour of sedentary behaviour per day was associated with a 30% multiplicative increase in the risk of hypertensive disorders of pregnancy, with risk rising steeply beyond 10 hours per day. This finding suggests that any reduction in sedentary time paired with an increase in light activity may represent a potentially beneficial strategy for cardiovascular health during pregnancy. 

What are the key take-home points?

1. Sitting less and moving more matters for blood pressure health during pregnancy.
2. In addition to meeting moderate-to-vigorous physical activity and sleep guidelines, aim for less than 8 hours of sitting per day and replace sitting time with light activity (standing and slow walking).
3. Light activity is accessible to nearly everyone, making it a practical target for prenatal counselling at any stage of pregnancy.

Future research should test whether interventions specifically designed to replace sitting with light movement can reduce the incidence of hypertensive disorders of pregnancy and improve long-term maternal cardiovascular health. These findings also highlight the importance of behaviours beyond structured exercise. For pregnant people who cannot meet moderate-to-vigorous physical activity guidelines, a sit less and move more pattern offers an additional and realistic target that clinicians can discuss during prenatal care. 

Authors: Alex H. Crisp, Kara M. Whitaker

References:

1. Ford ND, Cox S, Ko JY, et al. Hypertensive Disorders in Pregnancy and Mortality at Delivery Hospitalization – United States, 2017-2019. MMWR Morb Mortal Wkly Rep. Apr 29 2022;71(17):585-591. doi:10.15585/mmwr.mm7117a1
2. Davenport MH, Ruchat SM, Poitras VJ, et al. Prenatal exercise for the prevention of gestational diabetes mellitus and hypertensive disorders of pregnancy: a systematic review and meta-analysis. Br J Sports Med. Nov 2018;52(21):1367-1375. doi:10.1136/bjsports-2018-099355
3. Hesketh KR, Evenson KR. Prevalence of U.S. Pregnant Women Meeting 2015 ACOG Physical Activity Guidelines. Am J Prev Med. Sep 2016;51(3):e87-9. doi:10.1016/j.amepre.2016.05.023
4. Silva-Jose C, Sanchez-Polan M, Barakat R, Gil-Ares J, Refoyo I. Level of Physical Activity in Pregnant Populations from Different Geographic Regions: A Systematic Review. J Clin Med. Aug 8 2022;11(15)doi:10.3390/jcm11154638
5. Whitaker KM, Barone Gibbs B, Hivert MF, et al. Sedentary Behavior and Light-Intensity Physical Activity During Pregnancy and Cardiovascular Health: A Science Advisory From the American Heart Association. Circulation. May 13 2025;151(19):e990-e999. doi:10.1161/CIR.0000000000001316
6. Whitaker KM, Jones MA, Smith K, et al. Study Design and Protocol of the Multisite Pregnancy 24/7 Cohort Study. Am J Epidemiol. Feb 5 2024;193(3):415-425. doi:10.1093/aje/kwad208

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