Hydrops fetalis refers to the presence of two or more of the following abnormal fetal fluid collections:
- Pleural effusion
- Pericardial effusion
- Skin edema
Nonimmune hydrops fetalis (NIHF) comprises the subgroup of cases not caused by red cell alloimmunization (eg, Rh(D), Kell).
The widespread use of Rh(D) immune globulin has dramatically decreased the prevalence of Rh(D) alloimmunization and associated hydrops. As a result, NIHF now accounts for almost 90 percent of hydrops cases .
The incidence of NIHF ranges from 1/1500 to 1/3800 births [1-5]. Wide variations in reported incidence are due to differences in definitions, populations, and thoroughness of evaluation, as well as whether late pregnancy terminations were included.