Study design
This study was based on the data
from the Japan Environment and Children’s Study (JECS), which is a
nationwide government-funded prospective birth cohort launched in
January 2011 to investigate the effects of environmental factors on
children’s health.18,19 Briefly, the JECS is funded
directly by Japan’s Ministry of the Environment and involves the
collaboration between the Programme Office (National Institute for
Environmental Studies), Medical Support Centre (National Centre for
Child Health and Development), and 15 regional centers (Hokkaido,
Miyagi, Fukushima, Chiba, Kanagawa, Koshin, Toyama, Aichi, Kyoto, Osaka,
Hyogo, Tottori, Kochi, Fukuoka, and South
Kyushu/Okinawa).19 For inclusion as JECS participants,
expectant mothers had to meet the following criteria: (1) residence
within the study area at the time of recruitment and expectation to
continue residing in Japan for the foreseeable future; (2) expected due
date between August 1, 2011 and mid-2014; and (3) capacity to
participate in the study without difficulty (i.e., ability to comprehend
the Japanese language and complete a self-administered questionnaire).
There were two modes of recruitment: (1) at the time of the first
prenatal examination at participating obstetric facilities; and (2) at
local government offices issuing a pregnancy journal, called the
Maternal and Child Health Handbook, 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 history, physical
and mental health, lifestyle, occupation, environmental exposure at home
and in the workplace, housing conditions, and socioeconomic
status.19
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)18,19, and by the Ethics
Committees of all participating institutions. The JECS was conducted in
accordance with the Helsinki Declaration and other national regulations
and guidelines. Written informed consent was obtained from all
participating women.