Estimation of personal NO2 exposure in a cohort of pregnant women

There is a growing concern about the possible adverse effects of exposure to air pollution on health during pregnancy. Therefore, a priority of the INMA (environment and childhood) study was to estimate personal exposure to traffic-related air pollution. In the cohort from Valencia (n = 855), ambient levels of NO2 were measured at 93 sampling sites spread over the study area during four different sampling periods of 7 days each. Multiple regression models were used to map ambient NO2 over the area. Geographical data and predictions from kriging obtained by the “let one out” procedure were used as predictors. Individual exposure was assigned as 1) the estimated ambient NO2 level at the home address and 2) the average of estimated ambient NO2 levels at home and work addresses, weighted by the time spent in each environment. Estimations were temporally customised using the NO2 levels registered daily by the regional Air Pollution Monitoring Network. The entire pregnancy and each trimester were taken as exposure windows. The model for the mean levels of NO2 during the sampling periods explained 81% of the variation in NO2 levels. Relative percent differences between the two models of personal exposure assignment were less than 9% for more than 90% of the participants; however the rest of them showed marked differences. Personal exposure estimates were slightly higher in the second model. In both cases, exposure during the whole pregnancy was strongly correlated with exposure in the second trimester. Considering periods shorter than the entire pregnancy will provide us the opportunity to identify specific windows of susceptibility.