Comparison of physical activity during the second trimester of pregnancy based on differences in pre-pregnancy body shape perception: A cross-sectional study

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] <18.5 kg/m2 ) (Ministry of Health, Labour and Welfare, 2019). Body image distortion refers to the discrepancy between perceived and objectively assessed body shape. Body shape perception influences physical activity: negative emotions about one’s body are inversely associated with physical activity, while positive emotions are positively associated with it among adolescent boys and girls (Sabiston, et al., 2022). Moreover, pregnant women who reported high levels of exercise had greater body image satisfaction than those who reported low levels of exercise (Sun, et al., 2018). However, there is limited evidence regarding the relationship between pre-pregnancy body shape perception and physical activity during pregnancy. Moreover, to the best of our knowledge, no study has focused on the relationship between pre-pregnancy body image distortion and physical activity during pregnancy. Pregnant women often show reduced physical activity levels compared to non-pregnant women, often due to concerns about minor complications and the risk of miscarriage (Coll, et al., 2017), despite recent evidence showing that physical activity during pregnancy does not increase the risk of miscarriage, stillbirth, or delivery complications (Davenport, et al., 2019). The relevance of this finding is different for a woman who considers herself fat despite having a normal BMI as compared with a woman who considers herself overweight and also has a high BMI. In other words, when analyzing the exercise patterns of pregnant women, it is necessary to account for body image distortion rather than focusing only on actual BMI or body shape perception. Thus, we hypothesized that during the second trimester, pregnant women with a distorted body image might engage in moderate levels of physical activity to manage body weight gain. Generally, during the third trimester, the expansion of the abdomen may make it difficult to maintain moderate levels of physical activity. Therefore, it is necessary to investigate the relationship between pre-pregnancy body shape perception and physical activity levels during the second trimester. Against this background, our aims in this study, focused on the second trimester, were to compare physical activity based on differences in: 1) pre-pregnancy body shape perception, 2) pre-pregnancy BMI, and 3) the discrepancy between pre-pregnancy body shape perception and actual BMI. 2 Materials and Methods 2.1 Study design and participants Data for this cross-sectional study were derived from the Japan Pregnancy Eating and Activity Cohort Study, a multicenter study targeting pregnant and postpartum women across the Tohoku, Kanto, Kinki, and Kyushu regions. The University of Tokyo serves as the principal research institution, in collaboration with Yamagata, Osaka, and Kyushu universities. Participant recruitment began in February 2020 and is still ongoing. Pregnant women attending antenatal clinics at 13 weeks of gestation or less were recruited at clinics, hospitals, and university hospitals, and surveys were conducted during the second trimester (18–27 weeks), third trimester (34 weeks or later), and at 1, 6, and 12 months postpartum. Participants were asked to complete a 30-minute web-based questionnaire. The inclusion criteria for participants were age ≥18 years, ability to read and write in Japanese, and expectation of delivery at the health facility from which they were recruited. The exclusion criterion was being deemed unfit to participate by the medical staff. For this study, we used data from women who completed the second trimester 日本助産学会誌 Advance Publication by J-STAGE questionnaire by April 2023. Women who had been advised to rest by their obstetricians due to their complications or threatened preterm labor, were excluded from the analysis. 2.2 Measurement Demographic information, including employment status, level of education, marital status, and household income, as well as body shape perception and data from the Pregnancy Physical Activity Questionnaire, were extracted from second-trimester data. Information on age, pre-pregnancy BMI, and parity was obtained from medical records. Physical activity during the second trimester was assessed using the Pregnancy Physical Activity Questionnaire, developed by Chasan-Taber to evaluate physical activity in pregnant women (Chasan-Taber, et al., 2004). The reliability and validity of the Japanese version were evaluated by Matsuzaki (Matsuzaki, et al., 2010, 2014). The Japanese version consists of 36 items related to physical activity, covering five categories: household and childcare (13 items), transportation (4 items), occupation (5 items), sports and exercise (8 items), and inactivity (3 items). Based on intensity, activities are classified into four categories: vigorous (≥6.0 metabolic equivalents of task [METs]), moderate (3.0 – <6.0METs), light (>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