A prospective cohort study using thigh-worn accelerometers found that pregnant participants with lower sedentary time and more light-intensity activity across pregnancy had a lower risk of a composite adverse pregnancy outcome. The associations were generally similar after additional adjustment for moderate- to vigorous-intensity physical activity and prepregnancy body mass index, suggesting that lower-intensity movement during the rest of the day may be relevant to pregnancy health beyond structured exercise.
Participants in sedentary-behavior trajectory groups averaging roughly 10 to 12 hours per day had about twice the risk of adverse pregnancy outcomes compared with those averaging about 7 hours per day, according to a prospective multisite cohort study published in JAMA. Higher light-intensity physical activity and higher daily step-count patterns were associated with lower risk, although the highest step-count group was small and did not reach statistical significance for the composite outcome.
The Pregnancy 24/7 study enrolled 500 pregnant volunteers at less than 13 weeks’ gestation across 3 sites — the University of Iowa, the University of Pittsburgh, and West Virginia University — between 2021 and 2024. A total of 470 participants were included in the final analytic sample. The investigation was led by Bethany Barone Gibbs, PhD, FAHA, professor and chair of the Department of Epidemiology and Biostatistics at West Virginia University School of Public Health, and colleagues.
Participants wore an activPAL3 micro thigh-worn accelerometer for 7 days each trimester. The device allowed researchers to distinguish seated or reclined time from standing — a methodological advantage over wrist- or waist-worn devices, which cannot reliably separate sitting from standing still.
The composite primary outcome included hypertensive disorders of pregnancy (HDP), gestational diabetes (GD), preterm birth, and infants who were small for gestational age (SGA). Outcomes were abstracted from medical records and adjudicated by study physicians. At least 1 adverse pregnancy outcome occurred in 37% of participants, with HDP affecting 18%.
Key Findings
Researchers used group-based trajectory modeling to sort participants into 4 naturally occurring patterns — low, moderate, high, and very high — for each activity behavior across pregnancy. These groups were data-derived activity patterns, not validated clinical cutoffs.
After adjustment for age, parity, and socioeconomic status, participants in the high and very high sedentary patterns had more than twice the risk of the composite adverse pregnancy outcome compared with those in the low sedentary pattern. The low sedentary group averaged about 7 hours per day and had an adjusted absolute risk of 19%, whereas the high and very high sedentary groups averaged about 10 and 12 hours per day, respectively, and had adjusted absolute risks of about 42%.
Associations were observed for sedentary time accumulated in bouts of 60 minutes or longer, whereas shorter sedentary bouts were not significantly associated with outcomes.
Light-intensity physical activity (LPA) showed the opposite pattern. Compared with the low LPA pattern, which averaged about 3 hours per day and had an adjusted absolute risk of 40%, the very high LPA pattern, averaging about 7 hours per day, was associated with about half the risk of the composite outcome, with an adjusted absolute risk of 21%.
The signal appeared stronger for standing LPA than ambulatory LPA, particularly for HDP, although the mechanism and clinical meaning of this distinction remain uncertain.
Daily step patterns were also associated with risk. Compared with the low step-count pattern, which averaged about 3,900 steps per day and had an adjusted absolute risk of 48%, moderate and high step-count patterns were associated with a lower risk of the composite outcome. The moderate group averaged about 6,100 steps per day and had an adjusted absolute risk of 36%; the high group averaged about 8,500 steps per day and had an adjusted absolute risk of 32%.
The very high step-count group, averaging about 11,900 steps per day, showed a similar direction of association but did not reach statistical significance for the composite outcome, likely in part because the group was small.
Findings for HDP, the most prevalent individual outcome, were directionally similar to the composite. However, GD, preterm birth, and SGA events were too few to evaluate individually.
What Physicians Should Know
The study informs counseling conversations more than it changes practice. Current guidance continues to emphasize regular moderate-intensity aerobic activity during uncomplicated pregnancy. These findings suggest that lower-intensity movement during the rest of the day — particularly avoiding long uninterrupted periods of sitting — may be an additional area for research and counseling.
For patients who report barriers to moderate- or vigorous-intensity activity, such as fatigue, nausea, time constraints, or safety concerns, the data are consistent with a complementary “sit less, move more” counseling message. That message may include breaking up prolonged sitting, incorporating more standing, and accumulating steps throughout the day.
Importantly, the findings should not be translated into a specific prescription. The study does not establish a sitting-time limit, step target, or LPA dose that should be recommended clinically. Rather, it suggests that the overall pattern of daily movement may matter, even apart from structured exercise.
In an interview, Gibbs said the most important clinical takeaway is not a new numeric target but a low-risk counseling message about avoiding prolonged sitting.
“Our data suggest that a high sitting pattern may be associated with more outcomes. About half of the women in our study were sitting more than 10 hours/day, which seemed to be an important threshold. This finding is consistent with clinical data suggesting that activity restriction and bed rest are typically associated with worse — not better — pregnancy complications and are contraindicated by ACOG in most situations. Counseling pregnant women to avoid sitting for prolonged stretches and to generally sit less and move more is a low-risk recommendation that, based on our data, could possibly help prevent adverse pregnancy outcomes.”
Gibbs emphasized that the study should not be confused with research on exercise, because it focused on how participants spent nonexercise waking time.
The biggest misconception or nuance to this study is that we aren’t studying ‘exercise,’ something we call moderate- to vigorous-intensity physical activity. It is well known that, for most pregnant women, 20-30 minutes per day of moderate- to vigorous-intensity activity that increases your heart rate and makes you begin to sweat is recommended for a healthy pregnancy. Our study looked at something separate from that: what you are doing the other 15.5 hours/day, or the other 97% of the time you are awake. We found that women who spend most of the rest of that time sitting had twice as many adverse pregnancy outcomes.
This distinction may be especially relevant for patients who cannot consistently meet moderate-intensity activity goals or who spend much of the day seated because of fatigue, nausea, pain, work demands, long commutes, or working from home.
“Our study finds that simply sitting less and doing anything else — not necessarily intense exercise — is associated with major reductions in risk. This might be easier for pregnant women to achieve than exercise, and many women may be sitting a lot during pregnancy and not be aware or may think it’s OK — or even recommended. I hope our study brings awareness that lots of prolonged sitting for women could potentially lead to worse outcomes.”
The authors note that prior data on activity restriction or prescribed bed rest have raised concerns about worse pregnancy outcomes, although prescribed bed rest and habitual sedentary behavior are not equivalent exposures. Patients placed on activity restriction may differ substantially from lower-risk patients in observational cohorts.
Because the study was observational, it cannot establish that reducing sedentary time or increasing light-intensity activity will prevent adverse pregnancy outcomes. Randomized trials of “sit less, move more” interventions in pregnancy are needed before such strategies can be recommended as evidence-based clinical interventions.
What This Does Not Show
The study does not show causation. The design was observational, so residual confounding cannot be excluded. Patients with healthier pregnancies may be more able to move, stand, or accumulate steps, and not all relevant health, behavioral, or occupational factors may have been fully captured.
It also does not establish a validated threshold. The 7-, 10-, and 12-hour sedentary values were averages within data-derived trajectory groups. They should not be interpreted as validated clinical cut points.
The findings should not be assumed to apply equally to each component of the composite outcome. The primary endpoint included HDP, GD, preterm birth, and SGA, but only HDP occurred frequently enough for separate evaluation.
The study also does not prove definitive independence from BMI or exercise. Associations were generally similar after additional adjustment for moderate- to vigorous-intensity physical activity and prepregnancy BMI, but these were additional models, and some step-count associations were attenuated. The findings are best interpreted as suggesting that lower-intensity activity patterns may provide information beyond structured exercise, not as proving biological independence.
Generalizability is another limitation. Participants were predominantly White and tended to be healthy volunteers. Replication is needed in more racially and ethnically diverse populations and in patients with higher-risk pregnancies.
Finally, the study does not identify a mechanism. Why standing LPA appeared more strongly associated with lower risk than ambulatory LPA, especially for HDP, is unclear. The authors noted that mechanisms require further study.
Clinical Takeaway
For physicians, the practical message is cautious: current exercise recommendations during uncomplicated pregnancy remain unchanged, but patients’ nonexercise time may also matter. Encouraging patients to interrupt long sitting bouts, stand when feasible, and add light movement throughout the day is a low-intensity counseling message that may be particularly relevant for patients who cannot consistently meet moderate-intensity activity goals.
At the same time, the study should not be framed as proving that standing more or walking a certain number of steps prevents HDP, GD, preterm birth, or SGA. Its strongest contribution is to identify lower-intensity daily activity patterns as a promising, potentially practical target for future pregnancy intervention trials.
Disclosures and Funding
The study was funded by the National Institutes of Health (NIH; R01HL153095), the University of Iowa Institute for Clinical and Translational Science, the University of Pittsburgh Clinical and Translational Science Institute, and the West Virginia Clinical and Translational Science Institute. Several researchers reported receiving NIH grants during the conduct of the study; full disclosures are available with the published article. The funders had no role in study design, conduct, analysis, interpretation, manuscript preparation, or the decision to submit the manuscript for publication.
Source: JAMA
