Study design
In this study, we used the data
from the Japan Environment and Children’s Study (JECS), which is a
nationwide, government-funded, prospective birth cohort study that was
started in January 2011 to investigate the effects of environmental
factors on children’s health.22,23 Briefly, JECS is
funded directly by Japan’s Ministry of the Environment and involves
collaboration between the Programme Office (National Institute for
Environmental Studies), the Medical Support Centre (National Centre for
Child Health and Development), and 15 Regional Centres (Hokkaido,
Miyagi, Fukushima, Chiba, Kanagawa, Koshin, Toyama, Aichi, Kyoto, Osaka,
Hyogo, Tottori, Kochi, Fukuoka, and South Kyushu /
Okinawa).23 The eligibility criteria for expectant
mothers to participate in JECS were as follows: (1) residing in the
study areas at the time of recruitment and expected to continually
reside in Japan for the foreseeable future; (2) an expected delivery
date between August 01, 2011 and mid-2014; and (3) capable of
participating in the study without difficulty (i.e., able to comprehend
the Japanese language and complete the self-administered
questionnaires).
Either or both of the following recruitment protocols were applied: (1)
recruitment at the time of the first prenatal examination at the
cooperating obstetric facilities; and (2) recruitment at local
government offices issuing a pregnancy journal, called the Maternal and
Child Health Handbook, that is given to all expecting mothers in Japan
before they receive municipal services for pregnancy, delivery, and
childcare. We contacted pregnant women through cooperating health care
providers and/or local government offices issuing Maternal and Child
Health Handbooks and registered those willing to participate.
Self-administered questionnaires, which were completed by the women
during the first trimester and second/third trimester, were used to
collect information on demographic factors, medical and obstetric
history, physical and mental health, lifestyle, occupation,
environmental exposure at home and in the workplace, housing conditions,
and socioeconomic status.23
The JECS protocol was reviewed and approved by the Ministry of the
Environment Institutional Review Board on Epidemiological Studies on
March 23, 2010 (No. 15000141)22,23 and by the Ethics
Committees of all participating institutions. The JECS was conducted in
accordance with the principles of the Declaration of Helsinki and other
national regulations and guidelines. Written informed consent was
obtained from all participating women.