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Alloimmunization occurs in approximately one to two percent of pregnancies 1, though this estimate includes antibodies which are not clinically significant (see HDFN and the clinical impact of specific antibodies for a list of clinically significant antibodies). A recent retrospective observational study by Sánchez-Durán et al. in a large university setting identified maternal antibodies in 337 pregnancies in a fifteen-year period, of which 259 were clinically significant and known to have the potential to cause mild to severe hemolysis. Of these 259, the fetus was determined to be at risk (i.e., the fetus did inherit or had the potential to inherit the antibody’s target red blood cell antigen) in 194 2. Though RhD immune globulin (RhIG) prophylaxis is standard in developed countries, anti-D remains one of the most frequently identified antibodies (hence the name “Rh Disease”) along with anti-Kell (anti-K) and anti-E.
All pregnant patients should receive blood typing and an antibody screen (indirect Coombs test) during their first prenatal visit. The results of these screens present the following options for clinical management:
Once a patient’s antibody type and titer is established, the following sequence must take place to determine whether the fetus is at risk:
Read more about the necessary and optional laboratory assessments for the mother, father, and fetus.