Extended periods of sedentary behavior during pregnancy have been associated with negative health outcomes and unfavorable pregnancy results. This research aimed to pinpoint specific factors that could be targeted in efforts to reduce sedentary behavior among expectant mothers. Out of 103,057 pregnancies documented in the Japan Environment and Children’s Study, 83,733 participants were analyzed after removing repeated enrollments, missing responses, and incomplete outcome data. Sedentary behavior and activity levels were assessed using the International Physical Activity Questionnaire. Logistic regression was applied to estimate both unadjusted and adjusted odds ratios. To address missing data, multiple imputation techniques were used, and statistical computations were carried out with SAS software. The average daily sedentary time increased from 5.4 hours before pregnancy to 5.9 hours during pregnancy. The proportion of women classified within the high sedentary behavior category rose from 25.6% pre-pregnancy to 31.2% during pregnancy. Key factors linked to increased sedentary behavior included greater time spent watching television and playing video games prior to pregnancy, higher household income levels, and being employed during pregnancy. Conversely, engaging in at least 150 minutes of moderate to vigorous physical activity weekly before pregnancy was identified as a potential protective factor against elevated sedentary behavior. This large-scale cohort provides important insights into sedentary habits among pregnant women in Japan. Reducing sedentary time during pregnancy may be achieved by monitoring and limiting time spent on television and video games, along with fostering regular exercise habits before pregnancy.
