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Erythroblastosis
fetalis is hemolytic anemia in the fetus or neonate caused by transplacental transmission
of maternal antibodies to fetal RBCs. The disorder usually results
from incompatibility between maternal and fetal blood groups, often
Rh0(D) antigens. Diagnosis begins with prenatal
maternal antigenic and antibody screening and may require paternal screening,
serial measurement of maternal antibody titers, and fetal testing.
Treatment may involve intrauterine fetal transfusion or neonatal
exchange transfusion. Prevention is Rh0(D) immune
globulin injection for women at risk.
Erythroblastosis fetalis classically results from Rh0(D) incompatibility, which may develop when a woman with Rh-negative blood is impregnated by a man with Rh-positive blood and conceives a fetus with Rh-positive blood (see also Perinatal Hematologic Disorders: Hemolysis). Other fetomaternal incompatibilities that can cause erythroblastosis fetalis involve the Kell, Duffy, Kidd, MNSs, Lutheran, Diego, Xg, P, Ee, and Cc antigen systems, as well as other antigens. Incompatibilities of ABO blood types do not cause erythroblastosis fetalis.
Pathophysiology
Fetal RBCs move across the placenta to the maternal circulation throughout pregnancy. Movement is greatest at delivery or termination of pregnancy; in maternal abdominal trauma, fetomaternal hemorrhage may be marked. In women who have Rh-negative blood and are carrying a fetus with Rh-positive blood, fetal RBCs stimulate maternal antibody production against the Rh antigens (isoimmunization); the mechanism is the same when other antigen systems are involved.
In subsequent pregnancies, maternal antibodies cross the placenta and lyse fetal RBCs, causing anemia, hypoalbuminemia, and possibly high-output heart failure or fetal death. Anemia stimulates fetal bone marrow to produce and release immature RBCs (erythroblasts) into fetal peripheral circulation (erythroblastosis fetalis). Hemolysis results in elevated indirect bilirub in levels in neonates, which cause kernicterus in neonates (see Metabolic, Electrolyte, and Toxic Disorders in Neonates: Kernicterus). Usually, isoimmunization does not cause symptoms in pregnant women.
Diagnosis
and Treatment
At the 1st prenatal visit, all women are screened for blood and Rh type. If women have Rh-negative blood, the father's blood type and zygosity (if paternity is certain) are determined. If he has Rh-positive blood, maternal Rh antibody titers are measured at 26 to 28 wk. If titers are positive but < 1:32 (or below the value considered critical by the local blood bank), titers are measured more frequently. If titers are ≥ 1:32 (or above the local lab's crucial value), fetal middle cerebral artery blood flow is measured at intervals of 1 to 2 wk depending on titers and patient history; the purpose is to detect high-output heart failure. Elevated blood flow for gestational age should prompt percutaneous umbilical blood sampling (if anemia is strongly suspected) or biweekly spectrophotometric measurement of bilirubin levels in amniotic fluid (Δ ΟD450), obtained by amniocentesis. If paternity is reasonably certain and the father is likely to be heterozygous for Rh0(D), the fetus' Rh type is determined from amniotic fluid cells. If fetal blood is Rh negative or if middle cerebral artery blood flow or amniotic bilirubin levels remain normal, pregnancy can continue to term untreated. If fetal blood is Rh positive or unknown and if middle cerebral artery flow or amniotic bilirubin levels are elevated, suggesting fetal anemia, the fetus can be given intravascular intrauterine blood transfusions by a specialist at an institution equipped to care for high-risk pregnancies. Transfusions occur every 1 to 2 wk until fetal lung maturity is confirmed (usually at 32 to 34 wk), when delivery should be performed. Corticosteroids should be given before the 1st transfusion if the pregnancy is ≥ 24 wk.
Delivery should be as atraumatic as possible. Manual removal of the placenta should be avoided because it may force fetal cells into maternal circulation. Neonates with erythroblastosis are immediately evaluated by a pediatrician to determine need for exchange transfusion (see Perinatal Hematologic Disorders: Perinatal Anemia).
Prevention
Maternal sensitization and antibody production due to Rh incompatibility can be prevented by giving the woman Rh0(D) immune globulin. This preparation contains high titers of anti-Rh antibodies, which neutralize Rh-positive fetal RBCs. Because fetomaternal transfer and likelihood of sensitization is greatest at termination of pregnancy, the preparation is given within 72 h of termination of each pregnancy, whether by delivery, abortion, or treatment of ectopic pregnancy. The standard dose is 300 μg. A rosette test can be used to rule out significant fetomaternal hemorrhage, and if results are positive, a Kleihauer-Betke (acid elution) test can measure the amount of fetal blood in the maternal circulation. If fetomaternal hemorrhage is massive (> 30 mL whole blood), additional injections (up to five 300-μg doses within 24 h) are necessary. Treatment at termination of pregnancy is occasionally ineffective because sensitization may have occurred earlier during pregnancy. Therefore, at about 28 wk, all pregnant women with Rh-negative blood and no known prior sensitization are also given a dose. Because giving Rh0(D) immune globulin to sensitized women has no risks, the injection can be given when blood is drawn for titer measurement at 28 wk. Some experts recommend a 2nd dose if delivery has not occurred by 40 wk. Rh0(D) immune globulin should also be given after any episode of vaginal bleeding and after amniocentesis or chorionic villus sampling. Anti-Rh antibodies persist for > 3 mo after one dose.
Last full review/revision November 2005
Content last modified November 2005
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