Hydrops fetalis refers to edema of the fetus, involving subcutaneous edema, pleural effusion, pericardial effusion, and ascites. It can be caused by immune or non-immune factors, with the latter including genetic conditions, infections, tumors, and structural abnormalities. The document discusses the history, pathogenesis, diagnosis, and outcomes of hydrops fetalis. It provides overview of key figures in the study of this condition and reviews literature on rates, risk factors, and management approaches.