In the United States, anti-D immune globulin is given prophylactically to all D-negative, unsensitized women at approximately 28 weeks' gestation, and a second dose is given after delivery if the newborn is D-positive (American College of Obstetricians and Gynecologists, 2017). Before the 28-week dose of anti-D immune globulin, repeat antibody screening is recommended to identiy individuals who have become alloimmunized (American Academy of Pediatrics, 2017). Following delivery, anti-D immune globulin should be given within 72 hours. Recognizing that 40 percent of neonates born to D-negative women are also D negative, administration of immune globulin is recommended only after the newborn is conirmed to be D positive (American College of Obstetricians and Gynecologists, 2017). If immune globulin is inadvertently not administered following delivery, it should be given as soon as the omission is recognized, because there may be some protection up to 28 days postpartum (Bowman, 2006). Anti-D immune globulin is also administered after pregnancyrelated events that could result in fetomaternal hemorrhage (see Table 15-2).
Anti-D immune globulin may produce a weakly positive-1: 1 to 1 :4-indirect Coombs titer in the mother. This is harmless and should not be confused with development of alloimmunization. Additionally, as the body mass index increases above 27 to 40 kg/m2, serum antibody levels decrease by 30 to 60 percent and may be less protective (MacKenzie, 2006; Woelfer, 2004). D-negative women who receive other types of blood products-including platelet transfusions and plasmapheresis-are also at risk of becoming sensitized, and this can be prevented with anti-D immune globulin. Rarely, a small amount of antibody crosses the placenta and results in a weakly positive direct Coombs test in cord and infant blood. Despite this, passive immunization does not cause signiicant fetal or neonatal hemolysis.
It is estimated that in 2 to 3 per 1000 pregnancies, the volume of fetomaternal hemorrhage exceeds 30 mL of whole blood (American College of Obstetricians and Gynecologists, 2017). A single dose of anti-D immune globulin would be insuicient in such situations. If additional anti-D immune globulin is considered only for women with risk factors such as those shown in Table 15-2, then hafof those who require additional immune globulin may be missed. For this reason, all D-negative women should be screened at delivery, typically with a rosette test, followed by quantitative testing if indicated (American College of Obstetricians and Gynecologists, 20i17).
he rosette test is a qualitative test that identiies whether fetal D-positive cells are present in the circulation of a D-negative woman. A sample of maternal blood is mixed with anti-D antibodies that coat any D-positive fetal cells present in the sample. Indicator red cells bearing the D-antigen are then added, and rosettes form around the fetal cells as the indicator cells attach to them by the antibodies. hus, if rosettes are visualized, there are fetal D-positive cells in that sample. In the setting of D incompatibility, or any time a large fetomaternal hemorrhage is suspected-regardless of antigen status, a Kleihauer-Betke test or flow cytometry test are used. These are discussed on page 307.