Ambient air pollution affects birth and placental weight : a study from Lombardy (Italy)region

Rationale: The possible role of air pollution in adverse pregnancy outcomes has emerged in recent studies showing a relationship between high levels of air pollutants and low birth-weight (LBW), preterm delivery (PTD) and intrauterine growth restriction. LBW and PTD are the main responsible of perinatal morbidity and mortality in western countries. Importantly, the “fetal programming” hypothesis suggests that growth delay in-utero may influence also the risk of cardiovascular and metabolic diseases in adulthood. By now, results regarding the relationship between air pollution and fetal growth are partially discordant. Conflicting evidence may reflect inadequate control of confounders, variation in population characteristics, exposure assessment strategies and period of pregnancy considered. Methods: We investigated all singleton live births from mothers resident in Lombardy Region (Italy, 9.4 milion inhabitants) delivered by caesarean section in the largest Obstetric Hospital in Milan during the period 2004–2006 (n = 3692). Neonatal outcomes and maternal characteristics were derived from: i) regional recorded birth certificates and ii) clinical records. Birth-weight, head circumference, Apgar score, placental weight were the investigated outcomes. Detailed information about duration of gestation, baby gender, maternal age at delivery, parity, maternal illnesses, BMI and weight gain during pregnancy, parental education and occupation, were collected. Maternal air pollution exposure during pregnancy was estimated based on monitoring stations data from the Regional Environmental Protection Agency. Daily mean concentration of PM10, SO2, NO2, CO and O3 were obtained along with daily data on humidity and temperature. The region was divided in 9 areas with homogeneous average air pollution levels. Each woman was assigned to one area according to her residence at the time of delivery. Time variables were dealt with to represent the exposure time-window considered relevant for the different health outcome of concern. Effects were evaluated using multiple regression models controlling for the mentioned confounding factors. Results: Pregnant women were exposed to considerable levels of pollutant (mean PM10 = 49 Jg/m3, IQR = 26–63), with important seasonal variability (PM10 = 84 Jg/m3 in January and 23 Jg/m3 in August). We observed an inverse relationship between birth-weight and PM10 and NO2 exposure levels. The magnitude of the effect seems to vary according to windows of exposure during pregnancy: we observed a decrease of 12 and 8 grams in birthweight for 10 Jg/m3 increase in PM10 during the fourth and the fifth month of pregnancy respectively (P = 0.001 and P = 0.03). We also observed an increased risk of LBW (<2500 g) related to higher levels of exposure at fifth months of gestation (AdjOR = 1.006, P = 0.04 for PM10 and AdjOR = 1.012, P = 0.05 for NO2). PM10 and NO2 exposure during the two months before delivery resulted also associated with a decreased placental weight ([beta] for PM10 = -3, P = 0.03; [beta] for NO2 = -7, P = 0.02). CO seemed not to influence any of the Conclusions: Our preliminary results show that current air pollution levels in urbanised areas might affect fetal growth giving further support to rapid and efficient policy to decrease atmospheric pollutant levels.