Women who averaged about 7 hours of sedentary time per day instead of more than 10 hours and spent more time doing light activity had a significantly lower risk of adverse pregnancy outcomes, highlighting this as a potentially practical strategy beyond traditional exercise recommendations.
Study: Adverse pregnancy outcomes and sedentary behavior, light physical activity, and daily step count. Image credit: Maridav/Shutterstock.com
Recent research published in Japan Automobile Manufacturers Association They found that pregnant women who replaced several hours of daily sedentary time with light physical activity were less likely to experience adverse pregnancy outcomes.
How daily exercise shapes pregnancy health
Adverse pregnancy outcomes (APOs), such as hypertensive syndrome of pregnancy (HDP), gestational diabetes, preterm birth, and small-for-gestational age (SGA), affect approximately 1 in 5 pregnancies and can have immediate and long-term health consequences for both mother and child.
Although current evidence-based guidelines recommend moderate to vigorous physical activity during pregnancy, the role of low-intensity activities such as standing, light movements, and walking remains unclear. Pregnant women often feel tired or unmotivated to participate in such activities, and only about one in four women actually meet such guidelines.
These recommendations have recently been supplemented with guidance to get 30 minutes of moderate-to-vigorous physical activity each day, plus move more throughout the day and sit less. This means less time sitting and more time being active. Another recommendation is to walk 8,000 to 10,000 steps each day and encourage activity throughout the day, including light physical activity.
The researchers sought to determine whether reducing sedentary time and increasing time spent doing light activity throughout pregnancy could reduce the risk of these complications overall, and in particular of gestational hypertension (the only disorder with high enough prevalence in this sample).
Measures how you sit, stand, and how many steps you take each day
The study followed 470 pregnant women (mean age 31 years) who were recruited during the first trimester from university-affiliated medical centers in Iowa, Pennsylvania, and West Virginia. Participants wore thigh-worn activity trackers for seven days each semester, allowing researchers to measure sedentary time, light intensity physical activity (LPA), and daily step counts.
Sedentary time was categorized as total, short (less than 60 minutes sitting at one time), and long (more than 60 minutes sitting at one time). Similarly, light physical activity was stratified into total activity, standing activity, and walking activity.
The pregnancy outcome was later verified from medical records. Approximately 37% had an adverse pregnancy outcome and 18% developed gestational hypertension.
On average, all participants spent 10.1 hours per day sitting or lying down, 4.6 hours per day in light activity, and took an average of 6,783 steps per day. Sedentary women tended to be heavier, less likely to have given birth, less likely to be physically active, and take fewer steps per day.
Sitting for long periods of time has negative effects
Women who were sedentary for more than about 10 hours per day had about twice the risk of adverse pregnancy outcomes compared to women who were sedentary for an average of about 7 hours per day. This pattern persisted after adjusting for baseline body mass index (BMI) and moderate-to-vigorous activity.
After adjusting for age, parity, and socioeconomic status, the absolute risk of adverse pregnancy outcomes was 19% for women with low sedentary time, 42.3% for women with high sedentary time, and 41.6% for women with very high sedentary time.
Similar increases in risk were observed from short to long periods of sitting when only prolonged sitting was specified. Shorter sedentary periods were not associated with changes in outcome.
Increased daily movement leading to a healthier pregnancy
High activity levels were most common at 36.6%, while very high levels were found in only 10.6%. Women with higher levels of mild physical activity are more likely to have had children, have a lower body mass index (BMI), be less sedentary, take more steps each day, and engage in moderate to vigorous physical activity.
Very high levels of light activity were associated with a 48% reduction in risk of adverse pregnancy outcomes compared to low activity levels. The absolute risk was 21% for women with very high levels of mild activity and 40.3% for women with low activity levels.
Standing and doing light activity was most clearly associated with a lower risk of gestational hypertension. The adjusted absolute risk for HDP was 29.0% for those with low standing mild activity, 16.5% for those with high standing mild activity, and 10.8% for those with very high standing mild activity.
This corresponds to a 43% and 63% lower risk of these disorders for high or very high levels compared to low levels of standing activity, respectively.
Daily walking pattern predicts pregnancy outcome
More steps per day was also associated with a lower risk of adverse pregnancy outcomes. The adjusted risk decreased from 47.7% for women who took few steps, to 36.2% for women who took moderate steps, and 32.2% for women who took many steps.
A similar pattern of reduced risk was observed for gestational hypertension, with women in the high-step group having an approximately 54% lower risk than those in the low-step group. Sitting for long periods of time was similarly associated with poor prognosis, and light activity while standing was most clearly associated with a lower risk of gestational hypertension.
There was no difference in risk when only light activity during walking or short sitting time was analyzed.
Standing and moving throughout pregnancy
Certain patterns of low-intensity activity, such as decreased SED (sedentary time) (especially for long periods), increased LPA (light physical activity) (especially standing), and increased daily step count, were associated with clinically meaningful reductions in the risk of adverse pregnancy outcomes.
This association remained largely unchanged after accounting for moderate-to-vigorous exercise levels.
strengths and limitations
A strength of this study is the use of objective activity measures collected prospectively throughout pregnancy. In particular, the use of thigh-mounted activity monitors allowed researchers to distinguish between standing light physical activity and sedentary time, and was conducted in a population with varying socio-economic status and participants in both urban and rural areas. This confirms the results of a previous small study.
Because this study is observational, it cannot provide causal evidence that reduced sitting improves pregnancy outcomes. Most participants were Caucasian, healthy pregnant women, limiting generalizability to other ethnic groups and high-risk pregnancies.
Mechanistic studies can help understand the validity of this finding. More testing and development of such interventions compared with moderate to vigorous physical activity is needed to validate this approach.
During pregnancy: “Sit less and move more”
The results of this study suggest that a “sit less, move more” strategy is associated with a reduced risk of adverse pregnancy outcomes, particularly gestational hypertension. Optimizing activity patterns requires further development and testing as a practical method to improve pregnancy outcomes.
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