Rationale & Objective Several maternal chronic diseases have been reported as risk factors for congenital anomalies of the kidney and urinary tract (CAKUT) in offspring. However, these investigations used case-control designs, and cases with isolated genitourinary CAKUT were not distinguished from cases in which CAKUT were present with extrarenal congenital anomalies (complicated CAKUT). We examined the association of maternal diseases with isolated and complicated CAKUT in offspring using data from a prospective cohort study. Study Design A nationwide prospective birth cohort study. Setting & Participants 100,239 children enrolled in the Japan Environment and Children’s Study between January 2011 and March 2014 at 15 research centers. Physicians’ diagnoses in mothers and children were collected from medical record transcripts and questionnaires. Exposures Medical histories of maternal noncommunicable diseases, including obesity, hypertension, diabetes mellitus, kidney disease, hyperthyroidism, hypothyroidism, psychiatric disease, epilepsy, cancer, and autoimmune disease. Outcomes CAKUT diagnosed during the first 3 years of life, classified as isolated or complicated. Analytical Approach Multivariable Poisson regression with generalized estimating equations accounting for clustering by clinical center. Results Among the 100,239 children, 560 (0.6%) had CAKUT, comprising 454 (81%) isolated and 106 (19%) complicated forms. The risk of isolated CAKUT was increased in children of mothers who experienced kidney disease (adjusted risk ratio [RR], 1.80 [95% CI, 1.12-2.91]) or cancer (RR, 2.11 [95% CI, 1.15-3.86]). Furthermore, the risk of complicated CAKUT was increased in children of mothers with diabetes mellitus (RR, 3.04 [95% CI, 1.64-5.61]). Limitations Lack of standardization or prespecification of clinical definitions, diagnostic criteria, measurements, and testing. Genetic testing was not performed. Conclusions Isolated CAKUTs and complicated CAKUTs were associated with different maternal diseases. The results may inform clinical management of pregnancy and highlight potential differences in the genesis of isolated and complicated forms of CAKUT.

Background: Despite evidence for the protective effects of early regular exposure to peanut and egg proteins against allergies, the optimal timing of cow's milk (CM) protein exposure is unknown.Objective: We aimed to determine when during the first year of life CM‐based formula consumption becomes associated with lower CM allergy (CMA) risk.Methods: We used the data set of the Japan Environment and Children's Study (JECS), a nationwide birth cohort involving over 100 000 mother‐child pairs. CMA was defined as an allergic reaction to a CM product in an individual not consuming CM products at the time of evaluation, combined with physician‐diagnosed food allergy. For each exposure, we identified when formula milk was commenced, and its consumption status during 0‐3, 3‐6 and 6‐12 months old.Results: The prevalence of CMA was 0.23% and 1.03% at 6 and 12 months old, respectively. Multivariable regression analyses revealed that introducing regular consumption of formula within the first 3 months of age was associated with lower risk of CMA at 12 months. Regular consumption at 3‐6 months was strongly associated with a reduction in 12‐month CMA (adjusted relative risks [95% confidence intervals]: 0.22 [0.12‐0.35]), whereas no association was observed at 0‐3 months (1.07 [0.90‐1.27]).Conclusion and Clinical Relevance: Regular exposure to formula milk at age 3 months or older is associated with lower CMA at 12 months old, suggesting that the effect of very early CM exposure on CMA may disappear if the exposure is brief. At present, however, the results of this observational study should not be used for formula recommendation and randomized controlled trials are required to confirm this association.

Background: The association between a slower physical growth and poorer neurodevelopment has been established in infants born preterm or small for gestational age. However, this association is inconsistent in term-born infants, and detailed investigations in infancy, when intervention is most beneficial for improving outcomes, are lacking. We therefore examined this association separately by sex during the first year of life in term-born infants. Methods: Using data collected until children reached 12 months old in an ongoing prospective cohort of the Japan Environment and Children’s Study, we analyzed 44,264 boys and 42,541 girls with singleton term-birth. The exposure variables were conditional variables that disentangle linear growth from weight gain relative to linear growth, calculated from the length and weight at birth and 4, 7 and 10 months old. Neurodevelopmental delay was identified using the Japanese-translated version of Ages & Stages Questionnaires, third edition. Results: A reduced risk of neurodevelopmental delay at 6 months old was observed in children with a higher birth weight (adjusted relative risks [aRRs]: 0.91 and 0.93, 95 % confidence intervals [95 % CIs]: 0.87–0.96 and 0.88–0.98 in boys and girls, respectively) and increased linear growth between 0 and 4 months old (aRRs: 0.85 and 0.87, 95 % CIs: 0.82–0.88 and 0.83–0.91 in boys and girls, respectively). A reduced risk at 12 months was found in children with an increased linear growth between 0 and 4 months (aRRs: 0.92 and 0.90, 95 % CIs: 0.87–0.98 and 0.84–0.96 in boys and girls, respectively), boys with an increased relative weight gain between 0 and 4 months (aRR: 0.90, 95 % CI: 0.84–0.97), and girls with a higher birth weight (aRR: 0.89, 95 % CI: 0.83–0.96). Conclusions: These results suggest that a slow physical growth by four months old may be a predictor of neurodevelopmental delay during infancy.

Compared with the relatively well-investigated effects of childhood exposure to lead on neurocognitive deficits, those of prenatal exposure remain relatively inconclusive. We aimed to investigate the association between prenatal blood lead levels and neurodevelopmental delay during the first three years of life. From a prospective cohort of the Japan Environment and Children’s Study, we analyzed a total of 80,759 children. The exposure factors were prenatal lead concentrations measured from maternal whole blood in the second/third trimesters and umbilical cord blood at birth. Neurodevelopment was assessed at 6, 12, 18, 24, 30, and 36 months old using a screening tool, the Ages and Stages Questionnaires, third edition (ASQ). The outcome measures were any suspected neurodevelopmental delay (sNDD) identified via the ASQ during the first (sNDD-1Y), second (sNDD-2Y), and third (sNDD-3Y) years of life. sNDD-1Y, 2Y, and 3Y were identified in 18.0%, 16.2%, and 17.2% of children, respectively. The geometric means of blood lead concentration in this study were much lower (0.62 μg/dL in maternal blood and 0.50 μg/dL in cord blood) than previously investigated levels. Multivariable regression models revealed that there were no associations between maternal blood lead and sNDD-1Y and 2Y and between cord blood lead and sNDD-1Y, 2Y, and 3Y. Although a higher maternal blood lead was associated with a reduced risk of sNDD-3Y (adjusted relative risk: 0.84, 95% confidence interval 0.75–0.94, per 1 increase in common logarithm of lead concentration), there were no dose–response relationships in the analysis using quintiles of lead concentrations. Using a large-scale data set, the present study demonstrated no convincing evidence for an inverse association between levels of prenatal blood lead and neurodevelopment in early childhood. Longitudinal measurements of prenatal and postnatal lead levels are needed to understand the relationship between lead exposure and neurocognitive development.

Objectives To investigate the association between breast feeding and infant development during the first year of life using sibling comparison. Design Nationwide prospective birth cohort study with sibling pair analysis. Setting 15 regional centres that participated in the Japan Environment and Children’s Study. Participants This study included 77 119 children (singleton, term birth and no malformation/severe diseases) whose mothers were registered between January 2011 and March 2014, including 3521 duos or trios of siblings. Primary outcome measures The primary outcome was developmental delay at 6 and 12 months of age, assessed using the Japanese translation of the Ages and Stages Questionnaires, third edition. Multivariable regression analyses adjusted for confounders were performed to estimate the risk ratios of delay associated with any or exclusive breast feeding. Pairs of siblings discordant for statuses were selected, and conditional regression analyses were conducted with a matched cohort design. Results Developmental delay was identified in 6162 (8.4%) and 10 442 (14.6%) children at 6 and 12 months of age, respectively. Any breast feeding continued until 6 months or 12 months old was associated with reduced developmental delay at 12 months of age (adjusted risk ratio (95% CI): 0.81 (0.77 to 0.85) and 0.81 (0.78 to 0.84), respectively). Furthermore, exclusive breast feeding until 3 months was associated with reduced developmental delay at 12 months of age (adjusted risk ratio, 0.86 (95% CI 0.83 to 0.90)). In sibling pair analysis, the association between any breast feeding until 12 months and reduced developmental delay at 12 months of age persisted (adjusted risk ratio, 0.64 (95% CI 0.43 to 0.93)). Conclusions The present study demonstrated the association of continuous breast feeding with reduced developmental delay at 1 year of age using sibling pair analysis, in which unmeasured confounding factors are still present but less included. This may provide an argument to promote breastfeeding continuation.