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.