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The morbidity and mortality of Rh hemolytic disease can be significantly reduced by identification of women at risk for isoimmunization and by treatment of them with D immunoglobulin. Administration of D immunoglobulin [RhoGAM, Rho(D) immunoglobulin, RhIg] is very effective in the preventing isoimmunization to the D antigen.
Prenatal Testing
Routine prenatal laboratory evaluation includes ABO and D blood type determination and antibody screen. At 28-29 weeks of gestation woman who are D negative but not D isoimmunized should be retested for D antibody. If the test reveals that no D antibody is present, prophylactic D immunoglobulin [RhoGAM, Rho(D) immunoglobulin, RhIg] is indicated. If D antibody is present, D immunoglobulin will not be beneficial, and specialized management of the D isoimmunized pregnancy is undertaken to manage hemolytic disease of the fetus and hydrops fetalis.
Routine Administration of D Immunoglobulin
Abortion. D sensitization may be caused by abortion. D sensitization occurs more frequently after induced abortion than after spontaneous abortion, and it occurs more frequently after late abortion than after earlyabortion. D sensitization occurs following induced abortion in 4-5% of susceptible women. All unsensitized, D-negative women who have an induced or spontaneous abortion should be treated with D immunoglobu lin unless the father is known to be D negative.The dosage of D immunoglobulin is determined by the stage of gestation. If the abortion occurs before 13 weeks of gestation, 50 mcg of D immunoglobulin prevents sensitization. For abortions occurring at 13 weeks of gestation and later, 300-mcg is given.
Ectopic pregnancy can cause D sensitization. All unsensitized, D-negative women who have an ectopic pregnancy should be given D immunoglobulin. The dosage is determined by the gestational age, as described above for abortion.
Amniocentesis
It can occur after amniocentesis. D immunoglobulin, 300 mcg, should be administered to unsensitized, D-negative, susceptible patients following first- and second-trimester amniocente sis. These patients then receive routine antepartum and postpartum prophylaxis.
Following third-trimester amniocentesis, 300 mcg of D immunoglobulin should be administered. If amniocentesis is performed and delivery is planned within 48 hours, D immunoglobulin can be withheld until after delivery, when the newborn can be tested for D positivity. If the amniocentesis is expected to precede delivery by more than 48 hours, the patient should receive 300 mcg of D immunoglobulin at the time of amniocentesis.
Antepartum Prophylaxis
One to two percent of D-negative women become isoimmunized during the antepartum period. D immunoglobulin, administered both during pregnancy and postpartum, can reduce the incidence of D to 0.3%. Antepartum prophylaxis is given at 28-29 weeks of gestation.Antibody-negative, Rh-negative gravidas should have a repeat assessment at 28 weeks. D immunoglobulin (RhoGAM, RhIg), 300 mcg, is given to D-negative women. However, if the father of the fetus is known with certainty to be D negative, antepartum prophy laxis is not necessary.
Postpartum D Immunoglobulin
D immunoglobulin is given to the D negative mother as soon after delivery as cord blood findings indicate that the baby is Rh positive. A woman at risk who is inadvertently not given D immunoglobulin within 72 hours after delivery should still receive prophylaxis at any time up until two weeks after delivery. If prophylaxis is delayed, it may not be effective.
If there is any question about the amount of D immunoglobulin to be administered after delivery, a Kleihauer-Betke test should be performed in order to calculate the quantity of transplacental hemorrhage that has occurred. One vial (300 mcg) of D immunoglob ulin should be administered if the transplacental hemorrhage is 25 mL of blood or less, and two vials (600 mcg) are given if the transplacental hemorrhage is between 25 and 50 mL. The 300-mcg vial of D immunoglobulin protects against approximately 30 mL of fetal blood in the maternal circulation.
Treatment