|Use in Pregnancy|
As applied to pregnancy, RhIg's purpose is to prevent immunization to the D antigen in the perinatal period and thus prevent HDFN due to anti-D. If the mother has already produced anti-D, RhIg is of no use in moderating the immune response.Accordingly, RhIg is routinely administered to Rh negative women not previously sensitized to the D antigen under the following circumstances:1, Antenatal. Antepartum prophylaxis of 300 µg (1500 IU) at about 28 weeks gestation in the USA and Canada, which could be weeks later, depending on how appointments are scheduled. To illustrate variation in antenatal international practice, in the UK, smaller doses of RhIg (e.g., 500 IU) may be given at 28 weeks and 34 weeks, although many UK facilities issue a 1500 IU dose at 28–30 weeks. With antenatal administration, the Rh of the fetus is usually unknown. Some transfusion services recommend a further antenatal dose if the infant is undelivered after 40 weeks.2. Postnatal. Prophylaxis of 300 µg (1500 IU) at delivery of an Rh positive or weak D infant within 72 hours of delivery whenever possible. If RhIg administration is delayed beyond 72 hours, laboratory policies differ as to when it would no longer be administered. The longer the delay, the more likely RhIg may fail to suppress production of anti-D, but it is still worth trying. Note: Because RhIg contains IgG anti-D, when given antenatally, it can cross the placenta and sensitize fetal D-positive red cells. Occasionally the fetus may be born with a weakly positive DAT, but significant hemolysis does not occur. For this reason some guidelines recommend that labs do NOT routinely perform DATs on infants whose mothers have received antenatal RhIg.
Numerous studies have shown that, if administered correctly, RhIg is effective at preventing D immunization. To work, RhIg must be given in sufficient dose, and it must be given before Rh immunization has begun.Unfortunately, despite RhIg's proven efficacy, some women continue to make anti-D in the perinatal period. Such 'failures' are mainly (but not totally) due to human error. Examples of how women may still produce anti-D some 40+ years after the implementation of RhIg prophylaxis: Immunization to D occurred before the administration of RhIg, e.g., before 28 weeks gestation*; Immunization to D occurred after the administration of RhIg at 28 weeks and before delivery because an antenatal fetomaternal hemorrhage (FMH) occurred that was too large for residual passive anti-D to give protection; Female was already immunized from a prior pregnancy but anti-D was too weak to be detected in antibody screen tests prior to RhIg administration; RhIg dosage was insufficient to clear a larger fetal bleed at delivery (e.g., FMH screen was not done or a false negative occurred); Incorrect calculation of RhIg dosage; RhIg administered too late , e.g., well after 72 hours of delivery; Antenatal RhIg not given, e.g., mother had no, or limited, access to prenatal care, or did not seek it, and a FMH occurred during pregnancy; Failure of physician to carry out prenatal blood testing; RhIg not given due to laboratory clerical or technical error in Rh typing the mother or child; RhIg not given in cases such as abortions, ectopic pregnancies, and trauma (e.g., car accidents).* Because anti-D production before 28 weeks is rare (the order of 0.24% to 0.31%), RhIg's use earlier in pregnancy is not recommended. It is not cost effective and would expose most women to an unneeded blood product.
|Passive Anti-D following RhIg Administration|
A scenario where anti-D is detected at delivery in a female who received RhIg during pregnancy raises the question, is the anti-D active or passive?Distinguishing between passive and immune anti-D is important clinically: If passive anti-D is misinterpreted as active, RhIg prophylaxis may be omitted, leading to D sensitization. If active anti-D is misinterpreted as passive, appropriate antibody investigation may be curtailed putting the fetus at risk of developing HDFN.When this occurs, two main serologic questions need to be answered: Are the reactions due to passive anti-D from RhIg or due to active anti-D? Are there other antibodies that need to be excluded?
|Literature and Online Resources|
The following published literature and online resources, while useful, should not be used as a substitute for technical and clinical judgment. Medical and technical information becomes obsolete quickly and current sources relevant to the user's location should always be consulted.References indicated by * provide a broad overview of HDFN and are highly recommended.LITERATUREAvent ND, Reid ME. The Rh blood group system: a review. Blood 2000 Jan 15;95 (2):375-87.Bowman J. Thirty-five years of Rh prophylaxis. Transfusion 2003 Dec;43(12):1661-6.* Eder AF. Update on HDFN: new information on long-standing controversies. Immunohematology 2006;22(4):188–195. (scroll to article)Eder, AF, Manno, C.S. Alloimmune hemolytic disease of the fetus and newborn. In Wintrobe's Clinical Hematology, 11th ed. (Greer JP, Foerster J, Lukens JN, Rodgers GM, Paraskevas F, Glader BE, (eds). Philadelphia, PA: Lippincott, Williams & Wilkins, 2004.Flegel WA. Molecular genetics of RH and its clinical application. Transfus Clin Biol. 2006 Mar-Apr;13(1-2):4-12. Kennedy MS, McNanie J, Waheed A. Detection of anti-D following antepartum injections of Rh immune globulin. Immunohematology 1998;14(4):138-40.Koelewijn JM, de Haas M, Vrijkotte TG, van der Schoot CE, Bonsel GJ. Risk factors for RhD immunisation despite antenatal and postnatal anti-D prophylaxis. BJOG. 2009 Sep;116 (10): 1307-14. Epub 2009 Jun 17.* Kumar S, Regan F. Management of pregnancies with RhD alloimmunisation. BMJ. 2005 May 28;330(7502):1255-8. (UK perspective but much valuable information relevant to all)* Murray NA, Roberts IAG. Haemolytic disease of the newborn. Arch Dis Child Fetal Neonatal Ed 2007 Mar; 92(2): F83–F88. Oepkes D, Seaward PG, Vandenbussche FP, Windrim R, Kingdom J, Beyene J, Kanhai HH, Ohlsson A, Ryan G; DIAMOND Study Group. Doppler ultrasonography versus amniocentesis to predict fetal anemia. N Engl J Med. 2006 Jul 13;355(2):156-64.Ramsey G. Inaccurate doses of Rh immune globulin after Rh-incompatible fetomaternal hemorrhage: survey of laboratory practice. Arch Pathol Lab Med 2009 Mar; 133(3):465-9. Reid ME. The Rh antigen D: a review for clinicians. Blood Bulletin 2008 Apr; 10(1).Sandler SG. Effectiveness of the RhIg dose calculator. Arch Pathol Lab Med 2010 Jul;134(7): 967-8.Shulman IA, Calderon C, Nelson JM, Nakayama R. The routine use of Rh-negative reagent red cells for the identification of anti-D and the detection of non-D red cell antibodies. Transfusion 1994 Aug;34(8):666-70.Tamul KR. Determining fetal-maternal hemorrhage with flow cytometry. Advance 2000. Posted online June 5, 2000.Westhoff CM, Sloan SR. Molecular genotyping in transfusion medicine. Clin Chem 2008;54(12): 1948-50.ONLINE RESOURCESPaxton A. Bringing new rigor to RhIg calculations. CAP TODAY. May 2008. Accessed January 18, 2011.*Wagle S, Deshpande PG. Hemolytic disease of the newborn. eMedicine / WebMD. Updated Apr. 9, 2010. Accessed January 18, 2011.