The second phase of the Chiba Study of Mother and Child Health (C-MACH) was initiated to investigate how environmental exposures from the fetal period to early childhood influence maternal and child health outcomes. The sub-cohort focuses specifically on detailed assessments of indoor environmental factors and neighbourhood-built and social environments. By integrating environmental metrics with biological, behavioural and sociodemographic data, the study aims to elucidate their role in the development of allergies, neurodevelopmental disorders and other non-communicable diseases in early life.

Between June 2021 and April 2023, 505 pregnant women were enrolled in the second phase of the C-MACH main study. Of these, 298 participants consented to join the sub-cohort study, including 258 in the sleep and physical activity monitoring option (Option 1) and 148 in the indoor allergen exposure sub-study (Option 2). The study includes biological sampling, environmental monitoring and repeated questionnaire surveys. At baseline, 253 live births were recorded from 251 pregnancies.

Of the 298 women, 272 completed early pregnancy questionnaires. The mean maternal age was 33.1 years (SD 4.6); 97.8% were married. University-level education was reported by 51.0% of mothers and 53.7% of fathers. Most households had an annual income of 6 to

Longitudinal follow-up will continue until the children reach age 15. Future analyses will examine associations between environmental exposures and allergic, developmental, endocrine/metabolic and obesity-related outcomes.