••• Chapter 20^ Rh Alloimmunization^213
❍ At what hematocrit level is transfusion considered in the fetus remote from term?
<25%.
❍ At what gestation is intrauterine transfusion usually performed?
Intrauterine transfusion is usually performed between 18 and 35 weeks’ gestation.
After 35 weeks, delivery is generally considered safer than transfusion.
❍ Which antibodies to minor antigens have also been shown to result in fetal hemolytic disease?
Anti-E, anti-Kell (K1), anti-c, anti-c + E, anti-Fy (Duffy).
❍ Of the above, which minor antigen is the most common?
Anti-Kell (10% of people are Kell antigen positive).
❍ If a patient presents with anti-Kell antibodies, what two pieces of information should be obtained?
(1) Paternal Kell status.
(2) Question the patient if she has ever had a transfusion (Kell status is not checked for in transfused blood).
❍ What is the management of patients with antibodies to minor antigens?
Management is similar to Rh alloimmunization with measurement of maternal antibody titers, serial MCA
Doppler measurement or serial amniocenteses after a critical titer is reached, and transfusion or delivery based on
these results and gestational age. Because Kell sensitization causes suppression of fetal erythropoiesis as well as fetal
hemolysis, the ΔOD 450 is less predictive of the level of fetal anemia.
❍ What are the red blood cell surface antigens called that a fetus can inherit from the father?
Private antigens (a mother may become sensitized at first pregnancy and future pregnancies may develop
alloimmunization).
❍ What percentage of pregnancies are ABO incompatible?
20 to 25%.
❍ What blood types (maternal and fetal) cause most cases of ABO incompatibility?
O mother; A or B infant (mother has anti-A and anti-B IgG).
❍ Does ABO incompatibility require previous sensitization to affect the fetus?
No. ABO hemolytic disease may affect the firstborn child.