Physical Activity Before and During Pregnancy and Neurodevelopment in Early Childhood.

Importance: Prenatal maternal exercise is recognized for its benefits to both mother and child. However, research examining how maternal physical activity influences the neurodevelopment of offspring is limited. Objective: To investigate the association between maternal physical activity before and during pregnancy and neurodevelopmental outcomes in children. Design, Setting, and Participants: This cohort study analyzed data from the Japan Environment and Children's Study, a nationwide birth cohort funded by the Ministry of the Environment in Japan. Mother-child pairs were recruited and enrolled between January 24, 2011, and March 31, 2014, with child follow-up from birth to 3 years of age. Of 104 062 records, 65 843 were excluded due to missing data or guideline-based criteria, resulting in 38 219 mother-child pairs included in the analysis. The present analysis was conducted between June 24, 2024, and June 30, 2025. Exposures: Maternal physical activity levels were assessed before and during pregnancy using the International Physical Activity Questionnaire. Main Outcomes and Measures: Child neurodevelopment was assessed using the Ages and Stages Questionnaires, Third Edition, at 6-month intervals from 6 months to 3 years of age. Five developmental domains were evaluated: communication, gross and fine motor skills, problem solving, and personal-social. Scores were based on caregiver responses and compared with established cutoff scores. Results: Among the 38 219 mother-child pairs (maternal mean [SD] age, 31.1 [4.8] years; 19 429 [50.8%] male children), multivariable logistic regression showed that higher maternal physical activity was associated with child neurodevelopment. Higher prepregnancy activity was associated with significantly higher odds for each ASQ-3 domain at 6 months of age and higher midpregnancy activity with high odds for the gross motor (odds ratio [OR], 1.18; 95% CI, 1.06-1.33), fine motor (OR, 1.60; 95% CI, 1.37-1.86), and problem solving (OR, 1.23; 95% CI, 1.10-1.38) domains. Higher prepregnancy activity was associated with higher odds for the problem-solving domain (OR, 1.16; 95% CI, 1.01-1.34) at 3 years of age; there was no association with any other domain. Higher midpregnancy activity was not associated with higher odds of any ASQ domain at 3 years of age. Conclusions and Relevance: In this cohort study of mother-child pairs, maternal physical activity before and during pregnancy was associated with child neurodevelopment, particularly for motor function between 6 months and 1 year of age. Further investigations are required to find the physiological mechanisms explaining how maternal physical activity affects child neurodevelopment.