CXCR2 and hydrops fetalis: According to the results of correlation analysis, in HF, CCL2 was positively correlated with NK cells resting (r = 0.4036, p = 8.00E-05) and Mast cells activated (r = 0.3893, p = 0.0001) (Figure 7A), CXCR2 was positively correlated with neutrophils (r = 0.7338, p = 1.93E-16) (Figure 7B), and S100A9 was positively correlated with activated neutrophils (r = 0.5412, p = 3.64E-8) and Mast cell activated (r = 0.4635, p = 4.21E-06) (Figure 7C).