GSTM1 and hydrops fetalis: In contrast, for the deoxy-Hb signal, there was only a trend for the HF group mean Z score to differ from 0 (mean = 0.369, t(14) = 2.002, p = 0.065, d = 0.517), while the LF group was not significantly different from 0 (mean = −0.033, t(14) = 0.389, p = 0.702, d = 0.101).