The Modifying Role of Socioeconomic Position and Greenness on the Short-Term Effect of Heat and Air Pollution on Preterm Births in Rome, 2001-2013

Urban green spaces have been associated with health benefits, but few studies have evaluated the role of greenness on pregnancy outcomes. We examined how the association between short-term exposure to heat and air pollution on the probability of preterm delivery is affected by the spatial variation of socioeconomic position (SEP) and greenness. We analyzed a cohort of newborns in Rome, from April to October of 2001-2013, defining preterm as births between the 22nd and the 36th week of gestation. We used a time series approach, with maximum apparent temperature (MAT), PM10, NO2, and O-3 as exposure variables. As greenness indicators, we considered maternal residential proximity to green spaces and the Normalized Difference Vegetation Index (NDVI) within a 100 m buffer around each woman's residential address. We enrolled 56,576 newborns (5.1% preterm). The effect of a 1 degrees C increase in temperature on the daily number of preterm births was higher in women with low SEP (+ 2.49% (90% CI: 1.29-3.71)) and among those living within 100 m from green spaces (+3.33% (90% CI: 1.82-4.87)). No effect modification was observed for NDVI or PM10. SEP was an important effect modifier of the heat-preterm birth relationship. The role of greenness in modifying this association between heat and preterm delivery should be further investigated.