Lower placental iodine concentrations are linked with higher concentrations of ambient PM2.5 exposure during the last trimester of pregnancy.

Abstract

Background - The essential trace element iodine is needed for an optimal (neuro)-development of the fetus via the production of thyroid hormones. Recent findings indicate that exposure to ambient air pollution was linked with mild thyroid dysfunction during pregnancy. We hypothesize that air pollution might alter the placental iodine concentrations during gestation. Methods -We determined the placental iodine concentrations in 470 mother newborn pairs included in the ENVIRONAGE birth cohort. Maternal residential PM2.5 (particulate matter with a diameter < 2.5 µm), NO2, and black carbon concentrations were determined during the pregnancy using a high-resolution air pollution model. Using distributed lag nonlinear models (DLNM), we modeled the gestational week-specific association between placental iodine concentrations and air pollutants. Results - Significant inverse associations were observed between gestational exposure to PM2.5 at weeks 28 to 35 and placental iodine concentrations. Cumulative estimates over the trimesters of pregnancy showed that in the third trimester of pregnancy (week 27 until delivery) an increase of 5 µg/m³ in PM2.5 exposure was associated with a decrease of 0.85 µg/kg in placental iodine concentration (95%CI: -1.56 to -0.14). These associations were adjusted for maternal pre-pregnancy BMI, gestational weight gain, household smoking behavior, maternal alcohol consumption, maternal education, maternal age, vitamin use, gestational age, date and season at delivery, and newborns’ sex. No significance was found between placental iodine load and the ambient NO2 or black carbon exposure.Conclusions- Gestational exposure to PM2.5 is linked with a lower placental iodine concentration. This decrease indicates that ambient air pollution might interfere with the normal uptake mechanisms of iodine, which could results in worse neurocognitive health outcomes later in life.