Associations of physical activity and mental health in pregnant women: A cross-sectional isotemporal substitution analysis

Background: Prenatal mental health is an increasing public concern. At present, it has been shown that increasing physical activity (PA) is effective in promoting mental health of pregnant women. However, mental health may depend not only on the amount of time spent on a specific activity, but also on the intensity and type of the activity that it replaces. This study is aimed to explore the impact of replacing 60 min of one health behavior with another on the mental health of pregnant women. Methods: The cross-sectional study recruited 983 pregnant women from Chongqing, China between June and December 2021. The pregnant women self-reported their movement behaviors using the Pregnancy Physical Activity Questionnaire-Chinese version (PPAQ-C). Participants also completed three measures of mental health: Childbirth Attitudes Questionnaire (CAQ), 9-item Patient Health Questionnaire (PHQ-9) and the Positive affect sub-scale. An Isotemporal Substitution Model was used to evaluate mental health after replacing one movement behavior. Results: The analysis showed that replacing 60 min of sedentary behavior (SB) with moderate-to-vigorous intensity PA (MVPA) promoted positive emotions, and replacing SB with light intensity PA (LPA) reduced childbirth fear. Regarding PA types, replacing inactivity with household, occupational, or transport PA could reduce fear, and replacing inactivity, occupational, household or transport PA with sport PA could improve positive emotions and alleviate depression. Conclusion: An active pregnancy lifestyle with higher levels of moderate-to-vigorous physical activity and light physical activity and less sedentary behavior time and other inactive states may improve mental health. Future health promotion for pregnant women should consider the flexibility of physical activity types and intensities.