Baseline Profile of Participants in the Japan Environment and Children’s Study (JECS)

Abstract

INTRODUCTION

Publicity surrounding diseases caused by environmental pollution, such as Minamata disease (mercury poisoning) and Itai-Itai disease (cadmium poisoning),¹ ensures that most people know of the detrimental effects on health of highly concentrated chemicals. Japan is not as heavily polluted with such chemicals as it once was, but chemicals are still widely used; discussions now center on the effects of less concentrated chemicals in the environment on human health. The effects of environmental pollution on children’s health, in particular, is of international concern, and the topic has been discussed at the G7/G8 Environment Ministers’ Meeting.² In response, the Japanese Ministry of the Environment proposed a nationwide birth cohort study involving 100,000 mother-child pairs (and fathers, if accessible), and the Japan Environment and Children’s Study (JECS; Ecochil-Chosa in Japanese) was launched in 2011 to evaluate the effects of exposure to chemicals during the fetal stage and in early childhood on children’s health and development; follow-up is planned until the children are 13 years of age.³ Several secondary studies using data on approximately 10,000 women who gave birth in 2011 (the first year of recruitment) have already been published in peer-reviewed journals.^{4 –10}

Recruitment for the study was closed in March 2014, and the birth data were finalized for processing. This paper summarizes the baseline profiles of all participants (mothers, children, and fathers) at the start of the program.

METHODS

RESULTS

A JECS cohort flow chart from enrolment to delivery is shown in Figure 1. The study covers a total of 103,099 pregnancies. Excluding the 2,321 pregnancies with no subsequent delivery record, we were left with 100,778 pregnancies resulting in delivery, of which 51,402 (51.0%) involved program participation by male partners. Discounting pregnancies by the same woman, the study involved 95,248 unique mothers and 49,189 unique fathers. The 100,778 pregnancies involved 101,779 fetuses and resulted in 100,148 live births, 291 stillbirths (fetal deaths occurring at ≥22 weeks of gestation), and 1,340 miscarriages. It is difficult to accurately assess the coverage of the children (the number of live births registered in JECS divided by the number of all live births within the study areas) for the entire study period because we recruited women in early pregnancy and later expanded the study areas. In 2013, when recruitment was largely stabilized, however, the child coverage was approximately 45%.

Table 1 shows the response rates of the mothers, fathers, and children for each survey item. The questionnaire and medical record response rates were nearly 100%. The response rates for maternal blood and urine sampling were higher in the second/third trimesters (95.4% for blood and 95.6% for urine) than in the first trimester (88.7% and 88.5%, respectively), mainly because approximately 8% of the pregnancies were registered during the second/third trimesters. Since the first trimester questionnaire was also given to these late participants, its response rate was 98.5%. Although we prioritized the storage of cord blood samples in public cord blood banks, the samples collected from the mothers represented 87.3% of the pregnancies surveyed.

Baseline profiles of the mothers (mean age at delivery, 31.2; standard deviation [SD], 5.1) are shown in Table 2. Most were married (95.6%) and resided with their partner (and their child[ren]) (75.1%). The proportion of those who had received at least 13 years of education was 63.7% for the mothers and 55.8% for the fathers (mother-reported). The distribution of household income peaked at 2 to <4 million Japanese-yen/year (34.6%) and 4 to <6 million yen/year (33.1%). The mothers’ most common occupations in early pregnancy were homemaker (28.8%) and professional/engineering workers (22.3%). Smokers and alcohol drinkers during early pregnancy accounted for 18.2% and 45.9%, respectively. The distribution of baseline profiles did not substantially differ between the total population (about 100,000 mothers) and the sub-population of about 50,000 mothers with male partners participating in the study.

The mean age of the fathers when their partners gave birth was 32.9 (SD, 5.9) years (Table 3); 30.2% were engaged in the professional/engineering works, 47.7% had smoked during their partner’s early pregnancy, and 75.0% had drunk alcohol.

Table 4 shows baseline profiles of the 100,148 live births. The secondary sex ratio (male/female) was 1.05. Among the 98,259 singleton births, the mean anthropometric values at birth were weight: 3,023 (SD, 420) g, height: 48.9 (SD, 2.3) cm, head circumference: 33.2 (SD, 1.5) cm, and chest circumference: 31.8 (SD, 1.8) cm. The distributions of baseline profiles did not substantially differ between the total population (about 100,000 children) and the sub-population (about 50,000 children with participating fathers).

The baseline profiles of the mothers, fathers, and children for each Regional Centre are shown in eTable 2, eTable 3, and eTable 4.

DISCUSSION

We began registering the participants for the JECS in 2011 and completed registration in 2014, establishing one of the largest birth cohorts in the world. This paper outlines the baseline profiles of the JECS participants.

One strength of this study is that it covers the whole of Japan, from Hokkaido in the north to Okinawa in the south. Although the child coverage was approximately 45% in 2013, the selected characteristics of the mothers and children were comparable with those obtained in the national survey (Table 5).^{13 ,14} For example, the proportions of low birth weight (<2,500 g) were 8.2% for JECS in 2013 and 8.3% in the 2013 national Vital Statistics Survey.¹³ The fetal death rate in JECS (3.1 per 1,000 live births and fetal deaths at ≥22 weeks of gestation) was also similar to that in the national survey (3.0).¹³ Therefore, we think we can extrapolate the JECS results to the Japanese general population. Second, the large amount of information collected via questionnaires and/or medical records allows us to investigate the associations between environmental exposure and outcomes after controlling for many covariates, such as lifestyle and physical and social factors. Third, most of the participants provided bio-specimens during pregnancy and at delivery, which will be used to identify new substances in the environment posing health hazards and for gene analyses.

Some weaknesses also warrant consideration. First, only about half of the eligible men participated. However, the profiles of the mothers and children did not essentially differ between the total population and the sub-population with paternal participation. Another limitation is that the majority of women were recruited after the latter half of the first trimester. Therefore, we should keep in mind that we did not cover all early miscarriages. In addition, in spite of the large sample size, it is difficult to examine the associations of environmental exposure to chemicals with rare perinatal outcomes, such as amniotic embolism, sudden infant death syndrome, and many individual congenital anomalies.

Information about JECS is available to the public at http://www.env.go.jp/chemi/ceh/. We are following up the participating children by distributing guardian-administered questionnaires every 6 months, starting when the children become 6 months of age, and we are carrying out further chemical analyses of approximately 100,000 blood samples taken from mothers during their second/third trimesters for heavy metals, including lead, cadmium, mercury, manganese, and selenium; these analyses will be completed in 2017. We will soon be able to report on any associations of exposure to heavy metals during pregnancy with pregnancy and reproductive outcomes (eg, preterm delivery, birth weight, and secondary sex ratio).

ACKNOWLEDGEMENTS

We would like to express our gratitude to all of the JECS study participants and to the Co-operating health care providers. We also thank Ms. Masami Aya (National Institute for Environmental Studies, Tsukuba, Japan) for her technical assistance in summarizing the data, and the JECS staff members for their support. Finally, we gratefully acknowledge our indebtedness to the previous principal investigator for JECS, Dr. Hiroshi Satoh (Food Safely Commission, Cabinet Office, Tokyo, Japan).

The Japan Environment and Children’s Study was funded by the Ministry of the Environment, Japan. The findings and conclusions of this article are solely the responsibility of the authors and do not represent the official views of the above government.

Conflicts of interest: None declared.

APPENDIX A. SUPPLEMENTARY DATA

The following is the supplementary data related to this article:

eTable 1. Study area of each Regional Centre in the Japan Environment and Children’s Study, 2011–2014

eTable 2. Baseline profiles of the mothers according to Regional Centres in the Japan Environment and Children’s Study, 2011–2014

eTable 3. Baseline profiles of the fathers according to Regional Centres in the Japan Environment and Children’s Study, 2011–2014

eTable 4. Baseline profiles of the children according to Regional Centres in the Japan Environment and Children’s Study, 2011–2014

APPENDIX B.

Members of the Japan Environment and Children’s Study (JECS) as of 2016 (principal investigator, Toshihiro Kawamoto): Hirohisa Saito (National Centre for Child Health and Development, Tokyo, Japan), Reiko Kishi (Hokkaido University, Sapporo, Japan), Nobuo Yaegashi (Tohoku University, Sendai, Japan), Koichi Hashimoto (Fukushima Medical University, Fukushima, Japan), Chisato Mori (Chiba University, Chiba, Japan), Shuichi Ito (Yokohama City University, Yokohama, Japan), Zentaro Yamagata (University of Yamanashi, Chuo, Japan), Hidekuni Inadera (University of Toyama, Toyama, Japan), Michihiro Kamijima (Nagoya City University, Nagoya, Japan), Toshio Heike (Kyoto University, Kyoto, Japan), Hiroyasu Iso (Osaka University, Suita, Japan), Masayuki Shima (Hyogo College of Medicine, Nishinomiya, Japan), Yasuaki Kawai (Tottori University, Yonago, Japan), Narufumi Suganuma (Kochi University, Nankoku, Japan), Koichi Kusuhara (University of Occupational and Environmental Health, Kitakyushu, Japan), and Takahiko Katoh (Kumamoto University, Kumamoto, Japan).

REFERENCES

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.