Step-defined physical activity among pregnant and postpartum women: the 2003–2019 national health and nutrition survey of Japan

Although physical activity (PA) is beneficial for pregnant and postpartum women, there is limited objectively measured PA data during these critical life events in women’s health. Therefore, this study aimed to investigate age-adjusted steps/day in pregnant and postpartum women derived from a nationally representative sample. Pregnant and postpartum women ≥ 20 years of age were identified from the 2003–2019 National Health and Nutrition Examination Survey of Japan. Pregnancy or postpartum status was self-reported, and steps/day were assessed using pedometers. Additionally, a control sample of age-matched non-pregnant and non-postpartum women was randomly sampled from the same survey, based on the maximum feasible ratio across all ages. Age-adjusted steps/day were estimated using analysis of covariance and stratified by gestational age in trimesters (≤ 13, 14–27, ≥ 28 weeks), postpartum (early defined as < 6 months, late defined as ≥ 6 months and breastfeeding) status, maternal age group (20–29, 30–39, and ≥ 40 years), and employment status. The analytical sample comprised 575 pregnant women categorized into first (n = 139), second (n = 257), and third (n = 179) trimesters, respectively, 488 women in early postpartum, 697 women in late postpartum, and a 1:4 ratio of 7,040 randomly age-matched control group. Age-adjusted mean (standard error) steps/day for each of the trimester, postpartum (early and late), and control groups were 4,639 (299), 5,542 (220), 4,252 (263), 4,809 (160), 5,566 (134), and 6,939 (42) steps/day, respectively. The steps/day gradually increased by age category in the early postpartum period. Working women accumulated more steps/day than non-working women, especially in the first trimester (Δ = 1,459 steps/day, p = 0.007), whereas no employment status differences in steps/day were apparent in the third trimester or early postpartum period. Steps/day varied across trimesters of pregnancy and increased over the postpartum period. Overall, however, steps/day were approximately 1,400 to 2,700 steps/day lower throughout these maternal life events relative to a comparable general population of women. Despite distinct differences in accumulated steps/day throughout the trimester and postpartum periods, few current clinical and public health PA guidelines for pregnant and postpartum women consider trimester-specific considerations. Further studies are needed to determine the optimal PA recommendations relevant to specific pregnancy and postpartum periods.