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Erythrocyte Alloimmunization and Pregnancy

Overview

Maternal alloimmunization, also known as isoimmunization, occurs when a woman’s immune system is sensitized to foreign erythrocyte surface antigens, stimulating the production of immunoglobulin G (IgG) antibodies.

The most common routes of maternal sensitization are via blood transfusion or fetomaternal hemorrhage (ie, transplacental passage of fetal erythrocytes) associated with delivery, trauma, spontaneous or induced abortion, ectopic pregnancy, or invasive obstetric procedures. Two recent studies found that intravenous drug abuse is also associated with alloimmunization.
 These antibodies can cross the placenta during pregnancies in alloimmunized women and, if the fetus is positive for these specific erythrocyte surface antigens, result in hemolysis of fetal erythrocytes and anemia. This, in turn, can lead to potentially disastrous consequences for the fetus, such as hydrops fetalis (seen below), a high-output cardiac failure syndrome. With the institution of antenatal Rhesus (Rh) D immunoglobulin prophylaxis, the frequency of maternal alloimmunization in Rh D–negative women has decreased significantly. ACOG recommends administering Rhesus Immunoglobulin to Rhesus negative patients with any event in pregnancy that increases risk of fetomaternal hemorrhage and at 28 weeks gestation. Pending fetal blood type, the patient should also receive Rhesus Immunoglobulin following delivery.

Fetal hydrops. Ultrasound image of edema of the sc

Fetal hydrops. Ultrasound image of edema of the scalp and face in a hydropic fetus.

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Additionally, advancements in fetal surveillance and treatment have allowed for successful outcomes for most affected fetuses. This article reviews the pathophysiology, diagnosis, and management of erythrocyte Rh D alloimmunization and includes a discussion of rarer erythrocyte antigens.

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