![]() It should not be assumed that an antibody present in a D negative woman is anti-D, even after RhIG therapy. ![]() If the antibody screen is positive at any time during pregancy, the blood group specificity of the antibody should be identified. Antibody screening is also necessary prior to antepartum transfusion. Regardless of D type, additional antibody screening in the third trimester is indicated when there is a history of significant antibodies, blood transfusions or traumatic deliveries. Routine testing for unexpected antibodies in the third trimester or at delivery rarely provides useful clinical information. Only 1 in every 1000 women develops new antibodies capable of causing HDN between the first and third trimesters. In most cases, Rh positive patients need be screened for antibodies only once during their initial visit. This antibody screen is not required by regulatory agencies and is probably not cost effective. The risk of a woman developing anti-D between the first trimester and 28 weeks gestation is very low, occuring in only 2 of every 1000 Rh negative pregnancies. The same ehnancement methods (LISS, PEG) used to detect unexpected antibodies during pretransfusion testing can be used for prenatal antibody detection.Īn additional antibody screen may be ordered for Rh negative women at 26 to 28 weeks gestation to determine if active immunity to D has developed, before administration of RhIG prophylaxis. Antiglobulin testing should be done with anti-IgG reagent to detect clinically significant antibodies that are capable of crossing the placenta and causing hemolytic disease of the newborn (HDN). Giving Rh immune globulin to these women is not harmful.Īll women, regardless of their D type, should be tested during each pregancy for clinically significant antibodies, ideally at their first obstetrician visit. The clinical implication of this change is that a few women who actually have weak expression of the D antigen will be classified as Rh negative and will be candidates for Rh immune globulin. All women are now typed as either Rh negative or positive. The main reason is that today’s blood typing reagents are much more potent and most of the patients who were previously typed as weak D are now typed as Rh positive. The AABB has determined that weak D testing is no longer necessary for obstetric patients. Historically, if a patient typed as Rh negative, additional testing was then performed to determine if they had weak D expression. Serologic confirmation of the D type is also recommended at the beginning of each subsequent pregnancy. This recommendation is especially important as a safeguard to prevent an Rh negative woman from being falsely typed as Rh positive and denied RhIG. A record of the maternal ABO type is also helpful should the newborn infant develop signs and symptoms consistent with ABO HDN.ĭ typing should be done on at least two separate occasions and the results should be identical. Any discrepant results must be fully investigated. The results should not conflict with historical records. ![]() ABO typing is done primarily for patient identification. Repeat at 2-4 week intervals if below critical titerĪll women should be tested for ABO and D as early as possible in pregnancy, preferably during their first trimester visit. Rh or other clinically signficant antibody 3 rd trimester if history of antibodies or transfusion ![]()
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