RBP4 and hydrops fetalis: Ultimately, among the differentially expressed proteins with significant concentration differences in the MCO period compared to the HF period, we selected four: fibronectin 1 (FN1), the nutritional indicator with the highest VIP score, complement component 4B (C4B), an inflammatory marker, retinol-binding protein 4 (RBP4), a contributor to insulin resistance, and fetuin B (FETUB), a hepatokine that is associated with glucose homeostasis.