CRP and hydrops fetalis: After excluding 3 SNPs (rs12567136, rs12740374 and rs9295128) with potential outliers and influential points, as well as, potential pleiotropy (11 SNPs), significant causal effect between CRP and HF was observed (Q = 317.55, p < 0.001; I2 = 37.6%; intercept = 0.003, p = 0.234; IVW, OR = 4.18, 95% CI = 3.40–5.13, p < 0.001) (Table 1, Additional file 1: Figure S2 and Figure S4).