Fetoplacental weight ratio in relation to PM2.5 exposure during the gestation in Tokyo, Japan

Abstract

BACKGROUND AND AIM: Some studies reported the association between particulate matter exposure during the gestation and placental weight. Because there is well correlation between placental weight and birth weight, it is no wonder that PM2.5 exposure was associated with placental weight as well as birth weight. However, we have little evidence whether PM2.5 exposure alters placental weight as a result of the disturbance of placental function. In this study, we examined the association of maternal exposure to PM2.5 and its components with placental weight and fetoplacental weight ratio that reflects placental function. METHODS: We collected birth records from the Japan Perinatal Registry Network database, and included all women without missing information, who delivered singleton term births in 23 Tokyo wards from 2013 to 2015. Using fine particles that collected everyday at one monitoring station according to the Federal Reference Methods, we analysed the chemical constituents of PM2.5, including organic carbon, elemental carbon, and ions (nitrate, sulphate, ammonium, chloride, sodium, potassium, and calcium). We estimated exposure to each pollutant over the first (0-13 gestational weeks), second (14-27 weeks), and third (28-36 weeks) trimesters, and examined the exposure-outcome association using multilevel linear regression models. RESULTS:We analysed 63,990 women (births) in this study. Total PM2.5 over the third trimester (mean concentration = 16.9 µg/m3) was not associated with placental weight, but the inverse association was observed for sulphate. Compared with the lowest quintile of sulphate concentrations, the adjusted differences of placental weight in the highest was -6.7g (95% CI = -12.5 to -0.9). No meaningful association was observed between PM2.5 and its components, and fetoplacental weight ratio. CONCLUSIONS:In this study, exposure to sulphate, one of major PM2.5 components, over the third trimester reduced placental weight. Further studies are needed to elucidate whether PM2.5 exposure leads to placenta functional disturbance. KEYWORDS: Air pollution, Particulate matter, Particle components, Birth outcomes, Environmental epidemiology