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Key Points

  • Immune hydrops is a serious condition in which abnormal fluid collections accumulate in at least two different fetal compartments, and in which circulating antibodies against red cell antigens are detected in the mother.

  • If a first-time mother is Rh negative and her fetus is Rh positive, there is a 16% risk that the fetal Rh antigen will stimulate the maternal immune system to produce anti-D antibody.

  • Isoimmunization due to non-Rh(D) and non-ABO incompatibility usually occurs as a result of blood transfusions, and atypical antibodies develop in approximately 1% to 2% of recipients.

  • Fetal anemia secondary to Kell isoimmunization differs from that due to Rh(D) isoimmunization because the mechanism for the anemia is most likely erythroid suppression rather than hemolysis.

  • Immune and nonimmune hydrops can be differentiated by maternal indirect Coombs test to screen for antibodies associated with blood group incompatibility.

  • Immune hydrops should be considered an emergency, and arrangements should be made to promptly perform percutaneous umbilical blood sampling (PUBS) and possibly fetal blood transfusion or immediate delivery depending on gestational age.

  • Blood for PUBS should be group O red cells, packed to a hematocrit of approximately 80%, less than 4 days old, irradiated, anti-cytomegalovirus negative, negative for the antigen to which the mother is immunized, and Kell negative.

  • It is generally not a good idea to transfuse a hydropic fetus to a final hematocrit that is greater than 25% or greater than four times the initial hematocrit, as this has been associated with fluid overload and sudden intrauterine fetal death.

  • The optimal mode of delivery for the hydropic fetus is uncertain, although cesarean delivery is usually considered safer to decrease the risk of soft-tissue trauma.

  • Minimal data are available regarding the long-term outcome of surviving fetuses that had immune hydrops.

  • The recurrence risk for immune hydrops is significant. In general, the more severe the obstetric history of rh isoimmunization, the more likely the recurrence risk for severe disease in the future.


Immune hydrops fetalis is a serious fetal condition in which abnormal fluid collections accumulate in at least two different fetal compartments, and in which circulating antibodies against red cell antigens are detected in the mother. Hydrops fetalis is associated with a pathologic increase in interstitial and total fetal body water, usually appearing in fetal soft tissues and serous cavities. The cause may be either immunologic or nonimmunologic, depending on the presence or absence of maternal antibodies against fetal red cell antigens. While previously it was considered that the majority of cases of hydrops fetalis were secondary to maternal–fetal blood group incompatibilities, it is now estimated that the causes are nonimmunologic in more than 90% of cases (see Chapter 128) (Santolaya et al., 1992).


Immune hydrops is most likely a result of maternal–fetal Rhesus (Rh) blood group incompatibility, in which maternal antibodies to certain fetal blood group antigens cross the placenta, causing hemolysis of ...

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