MPO and hydrops fetalis: In SWS, the activity of MPO (↑68.89%, p = 0.0005; ↑68.89, p = 0.0004, respectively) and the concentration of peroxynitrite (↑68.46%, p < 0.0001; ↑55.63%, p < 0.0001, respectively) and nitrotyrosine (↑73.15%, p = 0.0101; ↑63.97%, p = 0.0029, respectively) were significantly higher in the group of HF patients with NS and HS compared to the controls.