GSTM1 and hydrops fetalis: In GSTM1–wild-type subjects, the estimated decreases in HRV for a 10-μg/m3 increase in PM2.5 were 2.0% (95% CI, −11.3 to 8.3; p = 0.69) for SDNN, 4.0% (95% CI, −24.8 to 22.6; p = 0.74) for HF, and 0.6% (95% CI, −19.0 to 22.0; p = 0.95) for LF.