Prenatal phthalate exposure and early childhood asthma: a prospective birth cohort study from the Japan Environment...

Prenatal phthalate exposure has been associated with allergic outcomes; however, evidence linking it to childhood asthma remains inconsistent. Using data from the Japan Environment and Children's Study (JECS), we examined the association between prenatal phthalate exposure measured during the first and second/third trimesters and current asthma in early childhood.

Among 9,707 mother-child pairs with urinary phthalate measurements in both the first and second/third trimesters, 8,554, 8,048, and 7,722 singleton children with available asthma data were analyzed at ages 2, 4, and 6 years, respectively. Current asthma was defined as wheezing in the past 12 months together with caregiver-reported physician-diagnosed asthma during that period (or ongoing asthma treatment). In the primary analyses, first-trimester, second/third-trimester, and average concentrations were analyzed using logistic regression adjusted for maternal allergy or asthma history, smoking, education, household income, parity, and recruitment center, with multiple imputation and false discovery rate (FDR) correction. Additional analyses included sex stratification, generalized estimating equations, mutually adjusted trimester-specific models, alternative asthma definitions, and quantile g-computation.

Current asthma prevalence was 6.4, 5.8, and 4.4% at 2, 4, and 6 years, respectively. In the primary analyses, no associations remained statistically significant after FDR correction. Similarly, generalized estimating equation and quantile g-computation analyses showed no significant overall associations after FDR correction. In additional analyses after FDR correction, the average monomethyl phthalate (MMP) concentration was positively associated with International Study of Asthma and Allergies in Childhood (ISAAC)-defined asthma at age 2, while first-trimester and average MMP concentrations were positively associated with later-confirmed age-2 asthma. These findings were not consistently observed across ages or analytic approaches.

Prenatal phthalate exposure was not consistently associated with current asthma in early childhood in this large Japanese birth cohort. Although certain MMP associations emerged in secondary and sensitivity analyses, the overall pattern of findings did not support a robust association.