Study design
In the present study, we used data from the JECS, which is a nationwide, government-funded birth cohort study.16 The JECS investigates the effects of environmental factors on children’s health by tracking mothers and their children until the children reach 13 years of age. From January 2011 to March 2014, 103,062 pregnancies were included in the JECS at 15 Regional Centres in Japan (Hokkaido, Miyagi, Fukushima, Chiba, Kanagawa, Koshin, Toyama, Aichi, Kyoto, Osaka, Hyogo, Tottori, Kochi, Fukuoka, and South Kyushu/Okinawa). Caregivers completed questionnaires regarding the mothers and their children during pregnancy and when the children were 6 and 12 months of age. The JECS protocol was reviewed and approved by the Ministry of the Environment’s Institutional Review Board on Epidemiological Studies and Ethics Committees of all participating institutions. The JECS was conducted in accordance with the Declaration of Helsinki and other nationally valid regulations and guidelines. Written informed consent was obtained from all participants.