Fetal-maternal haemorrhage

Medical condition involving the transfer of fetal blood cells into the maternal circulation

Fetal-maternal haemorrhage (FMH) is a medical condition that occurs when fetal blood cells cross the placenta and enter the maternal circulation. This phenomenon can have significant clinical implications, particularly in the context of Rh incompatibility and other blood group incompatibilities.

Pathophysiology

FMH can occur during pregnancy or delivery. The placenta, which normally acts as a barrier between the maternal and fetal blood supplies, can allow fetal red blood cells to pass into the maternal circulation under certain conditions. This transfer can happen due to trauma, placental abruption, or during normal labor and delivery.

The amount of fetal blood that enters the maternal circulation can vary significantly, from a few milliliters to more than 30 mL. In most pregnancies, small amounts of fetal blood enter the maternal circulation without causing any problems. However, significant FMH can lead to maternal sensitization to fetal antigens, particularly the RhD antigen, resulting in hemolytic disease of the newborn in subsequent pregnancies.

Clinical Significance

FMH is particularly important in Rh-negative mothers carrying an Rh-positive fetus. If fetal red blood cells enter the maternal circulation, the mother may produce antibodies against the Rh antigen. These antibodies can cross the placenta in future pregnancies and attack the red blood cells of an Rh-positive fetus, leading to hemolytic disease of the newborn.

Diagnosis

The diagnosis of FMH can be made using several laboratory techniques. The most common method is the Kleihauer-Betke test, which involves staining maternal blood samples to identify fetal red blood cells.

Kleihauer-Betke test showing fetal red blood cells

In this test, fetal red blood cells appear as bright pink cells against a background of pale maternal cells. The test can estimate the volume of fetal blood in the maternal circulation, which is crucial for determining the need for interventions such as Rho(D) immune globulin administration.

Management

The management of FMH depends on the volume of fetal blood that has entered the maternal circulation and the Rh status of the mother. In Rh-negative mothers, the administration of Rho(D) immune globulin can prevent sensitization. This prophylactic treatment is typically given at 28 weeks of gestation and within 72 hours of delivery if the newborn is Rh-positive.

In cases of massive FMH, the fetus may require intrauterine transfusions to manage anemia. Postnatally, affected newborns may need phototherapy or exchange transfusions to treat hyperbilirubinemia and anemia.

Prevention

Preventive measures for FMH focus on minimizing trauma during pregnancy and delivery. Routine administration of Rho(D) immune globulin to Rh-negative mothers has significantly reduced the incidence of hemolytic disease of the newborn due to Rh incompatibility.

Related pages

• Rh disease
• Hemolytic disease of the newborn
• Kleihauer-Betke test
• Rho(D) immune globulin