As shown in Figure 1, the receiver operating characteristic (ROC) analysis indicated an estimated value of area under the curve for serum FGF21 level predicting advanced HF equal to 0.70 (95% CI: 0.60–0.79) and an optimal cut-off value based on the Youden index of 377.50 ng/mL, with a sensitivity of 70% (95% CI: 55.39–82.14%), specificity of 65.67% (95% CI: 53.06–76.85%), PPV of 60.34% (95% PPV: 47.35–74.99%) and NPV of 74.58% (95% CI: 60.95–83.58%). The gene discussed is FGF21; the disease is hydrops fetalis.