Effect of ambient air pollution and temperature on the risk of stillbirth: a distributed lag nonlinear time series analysis.

Each 5-ppm increase in the mean daily SO2 in lag 0 increased the risk of stillbirth by 6% while other air pollutants had no significant effects on stillbirth. In lags 0 and 1, the heat increased the risk of stillbirth while the cold had protective effects, which were not statistically significant.