Methods
In the present study, we investigated the data of the Japan Environment and Children’s Study (JECS), which is a nationwide, government-funded, birth cohort study10 that was started in January 2011 to investigate the effects of environmental factors on children’s health. The eligibility criteria for the JECS participants (expectant mothers) were as follows: (1) residing in one of the study areas at the time of recruitment and expected to reside continually in Japan for the foreseeable future, (2) an expected delivery date between August 01, 2011 and mid-2014, and (3) the ability to participate in the study without difficulty (i.e., the participant needed to be able to comprehend the Japanese language and complete the self-administered questionnaires). This study was conducted in 15 Regional centers across Japan as described previously.10 The JECS protocol was reviewed and approved by the Ministry of the Environment’s Institutional Review Board on Epidemiological Studies and by the ethics committees of all participating institutions. The JECS was conducted in accordance with the principles of Declaration of Helsinki and other nationally valid regulations and guidelines. Written informed consent was obtained from all participating women. There was no patient and public involvement in this study.