CD4 and hydrops fetalis: To assess the causal relationship between different lymphocyte subsets and HF risk, further MR analyses were performed on absolute counts of different lymphocyte subsets, including HLA-DR+ natural killer absolute count (AC), resting CD4 regulatory T-cell AC, CD8+ natural killer T-cell AC, secreting CD4 regulatory T-cell count, CD8+ T-cell AC, and CD39+ CD4+ T-cell AC, B cell AC, Memory B cells AC, Naive-mature B cells AC, and IgD+ CD38+ B cells AC.