Objectives This study aimed to compare physical activity levels during the second trimester of pregnancy according to differences in pre-pregnancy body shape perception. Method Demographic information and data from the Pregnancy Physical Activity Questionnaire were extracted from the second-trimester dataset of the Japan Pregnancy Eating and Activity Cohort Study. Based on body shape perception, pre-pregnancy body mass index (BMI), and the discrepancy between body image and BMI, participants were divided into three groups. Metabolic equivalents of task (MET)-hours per week were then compared by activity intensity and activity type. Results Of the 1489 pregnant women who consented to participate, data from 970 women were analyzed. Light-intensity physical activity was significantly more common among women who perceived their pre-pregnancy body shape as overweight rather than underweight. Moreover, household/caregiving physical activity was significantly less common among women who perceived their pre-pregnancy body shape as underweight compared to those who perceived it as normal or overweight. Physical activity levels across eight categories of activity intensity and type did not significantly differ among the three pre-pregnancy BMI groups. When comparing physical activity levels based on the presence or absence of a discrepancy between body shape perception and actual BMI, household/caregiving physical activity was significantly less common among women whose perception was appropriate rather than overestimated. Conclusion This study revealed that physical activity during the second trimester varies according to pre-pregnancy body shape perception. These findings may help inform strategies to promote physical activity among pregnant women. Key words: pregnant women, physical activity, body shape perception, body mass index, Japan Received 12 August 2025; accepted 22 December 2025; published online 10 April 2026 ＊1 Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University ＊2 Department of Midwifery and Women’s Health, Division of Health Sciences and Nursing, Graduate School of Medicine, The University of Tokyo ＊3 Department of Clinical Nursing, Graduate School of Medical Science, Yamagata University ＊4 Department of Children and Women’s Health, Division of Health Sciences, Graduate School of Medicine, Osaka University ＊5 Department of Reproductive Health Nursing, Graduate School of Health Care Sciences, Institute of Science Tokyo ＊6 Department of Social and Preventive Epidemiology, School of Public Health, Graduate School of Medicine, The University of Tokyo Corresponding author: Naoko Hikita, Email: hikita.naoko.419@m.kyushu-u.ac.jp 日本助産学会誌 J. Jpn. Acad. Midwif. https:// doi.org/10.3418/jjam.JJAM-2025-0042 Advance Publication by J-STAGE Copyright © 2026 Japan Academy of Midwifery J. Jpn. Acad. Midwif. 1 Introduction Physical activity during pregnancy helps maintain both mental and physical health. The World Health Organization (WHO) recommends that all pregnant and postpartum women without contraindications engage in at least 150 minutes of moderate-intensity aerobic activity per week (WHO, 2020). Physical activity during pregnancy reduces the risk of excessive gestational weight gain, gestational diabetes, gestational hypertension or preeclampsia (Davenport, et al., 2018; Du, et al., 2019), low birth weight, and preterm delivery (Takami, et al., 2018); therefore, it is clear that physical activity during pregnancy benefits both the mother and fetus. Low body weight among young women due to distorted body image, especially among women in their 20s who are of childbearing age, is a persistent concern in Japan. In 2019, the Ministry of Health, Labour and Welfare reported that 20.7% of women in their 20s were underweight (body mass index BMI 1.5 – <3.0 METs), and sedentary (1 – ≤1.5METs) (Chasan-Taber, et al., 2023). The total physical activity score was calculated by multiplying the MET value for each activity by the reported duration of participation. Physical activity levels were analyzed by both activity type and intensity. 2.3 Operational definitions 2.3.1 Pre-pregnancy body shape perception Pre-pregnancy body shape perception was assessed using the question: “How did you feel about your body shape before this pregnancy?” from the second-trimester questionnaire. Response options included “fat,” “slightly fat,” “neither,” “slightly thin,” and “thin.” Participants who selected “fat” or “slightly fat” were categorized as “overweight,” those who selected “neither” were classified as “normal,” and those who selected “slightly thin” or “thin” were classified as “underweight.” 2.3.2 Pre-pregnancy BMI According to the World
KOZUMA et al. (Thu,) studied this question.