RBP4 and hydrops fetalis: Subgroup analysis revealed RBP-4 concentrations of 43.70 ± 9.15 μg/mL in HFpEF, 45.32 ± 11.19 μg/mL in HF with mid-range ejection fraction (HFmrEF), and 48.73 ± 13.39 μg/mL in HFrEF (p < 0.001).