Introduction

Hydrops fetalis is the presence of excess body water in the fetus resulting in skin edema coupled with effusions in the pleural, peritoneal, or pericardial space. Because most pregnancies in the United States include routine fetal assessment by ultrasound, most cases of hydrops will be recognized before birth. An associated abnormality can be diagnosed either ante- or postnatally in the majority of patients who have hydrops. The prognosis for survival is generally poor. Over 50% of fetuses diagnosed with hydrops die in utero, and of those that survive to delivery, over half will die postnatally despite aggressive support.

Immune hydrops

Immune hydrops is a late manifestation of the anemia that results from fetal erythrocyte destruction by transplacentally acquired maternal antibodies to fetal red-cell antigens. The severity of anemia necessary to disturb total body water is unpredictable, but a hematocrit of less than 20% is commonly associated with hydrops. Fetuses with an immune basis for their hydrops who are not treated with intrauterine red-cell transfusion face a significant risk of in utero death.

Historically, the most common antigen causing an antibody-mediated hemolytic anemia was the Rh D. Anemia as a function of sensitization to the D antigen is infrequent today because of the routine use of Rh immunoglobulin in the management of women who are Rh-D-negative. Sensitization to other red-cell antigens, including Kell, e, and c also causes fetal hemolytic anemia and results in immune hydrops.