NPPB and hydrops fetalis: In correlation analysis, the level of Nt-proBNP was associated with SDNN (r = −0.19, p<0.001), LF/HF ratio (r = −0.37, p<0.001), and LF (r = −0.29, p<0.001) but not HF (r = −0.04, p = 0.172) (figure 2).