Associations between prenatal exposure to indoor air pollution and ambient particulate matter with infant growth

Despite growing concern, the developmental effects of prenatal exposure to indoor and ambient particulate pollution remain poorly characterized. This study examined their individual and joint associations with infant growth. Embedded in the PKUBC-T birth cohort (initiated in June 2018, China), this study included 1068 mother-infant pairs. The PM₁ and PM_2.5 concentrations from the last menstrual period to delivery were predicted via a validated machine learning model, whereas PM_2.5 constituents' concentrations were derived via a modified Community Multiscale Air Quality Model. Indoor air pollution was assessed via questionnaires covering four dimensions. Infant growth was evaluated using body mass index (BMI) Z-scores and weight-for-length (WFL) Z-scores at one year, with overweight/obesity (OWOB) defined by World Health Organization standards. Generalized linear regression indicated that increased exposure to indoor air pollution was associated with elevated BMI Z-scores (β = 0.089, 95 % CI: 0.007, 0.171) and WFL Z-scores (β = 0.094, 95 % CI: 0.013, 0.176) in offspring. PM₁ and PM_2.5 also exhibited positive associations with these growth indicators. Infants whose mothers were exposed to higher levels of organic carbon (OC), elementary carbon (EC), NH₄⁺ and SO₄^2- had an elevated risk of overweight/obesity (OWOB). Stratified analyses revealed that joint exposure to PM₁ above the median and indoor air pollution was related to increased infant growth, despite nonsignificant multiplicative interaction effects. Similar joint effects were observed for indoor air pollution and PM_2.5, along with its constituents. This study highlights synergistic harms of combined indoor-outdoor air pollution on infant growth, reinforcing the need for integrated policies targeting indoor combustion and ambient PM reduction to safeguard early-life development.