Inadequate maternal iodine intake affects thyroid function and may impair fetal brain development. This study investigated the association between maternal iodine intake during pregnancy and neurodevelopmental delay in offspring at 1 and 3 years of age using a nationwide birth cohort: the Japan Environment and Children’s Study. We assessed dietary iodine intake during pregnancy using a food frequency questionnaire and child neurodevelopment using the Japanese translation of the Ages and Stages Questionnaire, Third Edition. The risk of delay (score below the cut-off value) for fine motor domain at 1 year of age was increased in the lowest quintile iodine intake group compared with the fourth quintile iodine intake group. The risk of delay for problem-solving at 1 year of age was increased in the lowest and second quintile iodine intake group and decreased in the highest quintile iodine intake group. The risk of delay for communication, fine motor, problem-solving, and personal–social domains at 3 years of age was increased in the lowest and second quintile iodine intake group compared with the fourth quintile iodine intake group, while the risk of delay for fine motor and problem-solving domains was decreased in the highest quintile iodine intake group. Low iodine intake levels in pregnancy may affect child neurodevelopment.

Maternal exposure to polychlorinated biphenyls (PCBs) during pregnancy is associated with a low birth weight; however, the congener-specific effects of PCB congeners are not well defined. In this study, we used maternal serum samples from the Chiba Study of Mother and Child Health (C-MACH) cohort, collected at 32 weeks of gestational age, to analyze the effects of PCB congener exposure on birth weight by examining the relationship between newborn birth weight and individual PCB congener levels in maternal serum (n = 291). The median total PCB level in the serum of mothers of male and female newborns at approximately 32 weeks of gestation was 39 and 37 ng g⁻¹ lipid wt, respectively. The effect of the total PCB levels and the effects of PCB congener mixtures were analyzed using a linear regression model and a generalized weighted quantile sum regression model (gWQS). The birth weight of newborns was significantly associated with maternal exposure to PCB mixtures in the gWQS model. The results suggest that exposure to PCB mixtures results in low newborn birth weight. However, specific impacts of individual PCB congeners could not be related to newborn birth weight.

Purpose: Epidemiological studies have reported that environmental factors from fetal period to early childhood can influence the risk of non-communicable diseases in adulthood. This concept has been termed the developmental origins of health and disease (DOHaD). The Chiba study of Mother and Child Health (C-MACH) is a DOHaD concept-based birth cohort study which started in 2014. This study aims to investigate the effects of genetic and environmental factors, particularly fetal and postnatal living environment, on children’s health. We also aim to identify candidate biomarkers for their health status. Moreover, the second phase study of C-MACH which was initiated in 2021 aimed at expanding the sample size, especially for gut microbiota and epigenomic analysis; it also aimed at clarifying the impact of the coronavirus disease 2019 (COVID-19) pandemic on children’s health. Participants: This study consists of four hospital-based cohorts. Women who were <13 weeks pregnant and their partners were enrolled in the study. All data and biological samples will be stored in the Chiba University Centre for Preventive Medical Sciences. Findings to date: A total of 561 women and their partners provided their consent to participate in this study. Of these women, 505 completed the questionnaire during the early gestational period. The mean age of the 505 women at enrolment was 33.0 (SD, 4.5) years. The mean prepregnancy body mass index (BMI) was 21.7 (SD, 3.6) kg/m², with 74.5% of the women having a BMI of 18.5–24.9 kg/m². About 5.2% of the women smoked cigarettes during the early stages of pregnancy. Future plans: The primary study outcomes are allergies, obesity, endocrine and metabolic disorders and developmental difficulties in children. Variables related to genome, metabolome, epigenome, gut microbiota and exposome will be evaluated as health-related factors. The relationships between these outcomes and the health-related factors will be analysed.

Fipronil, a widely used phenylpyrazole insecticide, is known to disrupt circulating thyroid hormone (TH) levels in rodents. Concentrations of fipronil and its metabolites (fipronil sulfone and fipronil sulfide) in serum samples collected in 2009–2011 were measured for 131 Japanese pregnant women by a sensitive and accurate liquid chromatography-tandem mass spectrometric method developed in our laboratory to relate TH levels. Fipronil sulfone was detected in all the subjects with the median being 21 ng/L (min–max: 6.8–89), but fipronil and fipronil sulfide were detected in none of the subjects (detection limit: 5.0 and 1.2 ng/L, respectively), indicating a rapid and exclusive oxidative conversion to fipronil sulfone upon exposure. The median concentration of fipronil sulfone was lower than those previously reported for general populations in other countries by one order of magnitude. There were no attributes or dietary habits of the subjects that significantly vary the serum fipronil sulfone concentrations. Multiple regression analyses found no significant association between serum concentrations of fipronil sulfone and free thyroxine- or thyroid-stimulating hormone levels, indicating the absence of adverse effects on circulating TH levels probably due to the lower exposure levels of the present subjects. The present result would be valuable for establishing a dose–effect relationship of fipronils in humans on population levels.

Background: Isoflavone (ISO) consumption during pregnancy may affect food allergy (FA) in offspring through estrogen‐like and other biological effects; however, this ISO–FA association in mother–child pairs remains elusive. Herein, the maternal ISO–childhood FA association was investigated using the Japanese birth cohort data. Methods: The data from the Japan Environment and Children's Study, including 86,012 and 75,307 mother–child pairs, with FA in children aged ≤1 year and 1–3 years, respectively, were analyzed. Maternal ISO consumption (total daidzein and genistein) was assessed using a food frequency questionnaire. Physician‐diagnosed FA data were obtained using questionnaires completed by caregivers. ISO consumption data was categorized into quartiles (Q1: reference), and the ISO–FA association was assessed through multivariable logistic regression analysis after adjusting for maternal age, educational level, smoking status, pre‐pregnancy body mass index, history of allergies, blood folic acid concentration, total energy intake, and infant feeding method up to 4 months of age. Results: Overall, FA cases in children aged ≤1 and 1–3 years were 6.6% and 12.1%, respectively. Maternal ISO consumption was negatively associated with FA in all children aged ≤1 year (Q3, adjusted odds ratio [aOR]: 0.91, 95% confidence interval [CI]: 0.84–0.99; Q4, aOR: 0.86, 95% CI: 0.79–0.93) and in those aged 1–3 years (Q3, aOR: 0.93, 95% CI: 0.88–0.99; Q4, aOR: 0.88, 95% CI: 0.83–0.95). Furthermore, in sex‐stratified analysis, a negative association was observed between maternal ISO consumption and FA in female children of all ages, whereas this inverse association was observed only in 1–3‐year‐old male children. Conclusions: Overall, the findings show that maternal ISO consumption during pregnancy may reduce the risk of childhood FA, exhibiting sex‐difference effects on offspring development.