Correlation analysis revealed that NT-proBNP levels were significantly related to both time and frequency domain indices (lnSDNN: Spearman ́s rho = -0.32, p = 0.001; lnSDANN: Spearman ́s rho: -0.33, p = 0.001; lnTP: Spearman ́s rho: -0.25, p = 0.01; lnVLF: Spearman ́s rho: -0.33, p = 0.001; lnLF: Spearman ́s rho: -0.35, p < 0.001; lnLF/HF: Spearman's rho: -0.34, p = 0.001). The gene discussed is NPPB; the disease is hydrops fetalis.