Secular trends in early motor development between 1980 and 2010 in Japan

Objective Recent changes in birth characteristics in Japan may have a potential influence on children's developments. Therefore, we investigated secular trends in gross motor milestones. Design Data were collected from an official Japanese nationwide serial cross-sectional survey conducted every 10 years since 1960. 22 320 participants aged 2-18 months were identified from the four surveys from 1980 to 2010. Outcomes We assessed whether or not a child achieved four gross motor milestones including rolling over (rolling), sitting without support (sitting), standing with support (standing) and walking alone (walking). The target age was defined as the age when the attainment rate ranged from >5% to >95% of the total. Multivariate logistic regression models were fitted. Results The final cohort included 20 570 children. The target ages were determined as follows: 3-6 months for rolling; 5-9 months for sitting; 6-11 months for standing; and 9-15 months for walking. The attainment rates of sitting, standing and walking in 1990 were higher than those in 2010, even after adjusting for child characteristics (sitting: adjusted OR (a0R)=2.07 (95% CI 1.62 to 2.65); standing: aOR=1.63 (95% CI 1.32 to 2.02); and walking: aOR=1.61 (95% CI 1.34 to 1.95)). Conclusions The proportion of children who attained three motor milestones (sitting, standing and walking) by set target ages decreased between 1990 and 2010. The contribution of birth characteristics including a decrease in gestational age and fetal growth, as well as changes in other child characteristics, failed to explain why this decrease occurred.