Rh-D Alloimmunization Prevention in the Emergency Department

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Summary and Quick Hits: Preventing Rh-D alloimmunization and Hemolytic Disease of the Newborn (HDFN) starts in the ED

  • As Emergency Physicians we can help to prevent HDFN by recognizing fetal-maternal hemorrhage and other sensitizing events in Rh-negative women and subsequently providing Anti-D immunoglobulin
  • Common risks for fetal maternal hemorrhage:
    • ectopic pregnancy
    • threatened miscarriage, missed abortion and miscarriage
    • antepartum hemorrhage
    • blunt abdominal trauma
    • delivery in Rh-negative females.
  • An Rh negative woman with a positive Indirect Coombs Test (screen) after administration of Rh-D immunoglobin should continue to be offered Rh-D immunoglobin (especially if the titer does not exceed 1:4)
  • Fetal Maternal Hemorrhage (FMH) quantification is not necessary at less than 20 weeks (< 16 weeks at UC Health).
  • All Rh D-negative women giving birth to Rh D-positive infants undergo testing for FMH quantification
  • Kleihauer–Betke test may not be accurate in conditions in which the mother has a coexistent medical condition that is associated with red blood cells containing an increased percentage of hemoglobin F, alternative methods, such as flow cytometry should be used

Approach to the undifferentiated female patient ED patient to limit risk of alloimmunization by maternal-fetal blood exposure and appropriate Rhogam use. Figure by Adam Gottula, MD (CC by 4.0)

Hemolytic Disease of the Newborn - What is it and why does it matter to Emergency Physicians:

Hemolytic Disease of the Fetus and Newborn (HDFN) is an alloimmune disease which develops in a fetus when a women’s immune system is sensitized, developing IgG antibodies against paternal antigens on the fetus’s red blood cells (RBCs). IgG antibodies have the ability to cross the placenta and attack fetal RBCs, resulting in a risk to any current or future fetuses with such antigens. When a mother is sensitized, the consequences can range from minimal to severe. In severe cases the fetus can develop a neonatal jaundice, kernicterus, or hemolytic anemia leading to high output fetal heart failure and ultimately hydrops fetalis. This often results in fetal death. (1) HDFN is most commonly triggered by the D antigen, expressed as part of the fetal red blood cell (RBC) membrane at 38 days, but can be caused by ABO incompatability and other antigens. ABO incompatability is less severe as the fetal RBCs express less of the ABO blood group antigens compared with adult levels. (2) Mothers are exposed to the fetal Rh D antigen when the syncytiotrophoblast and the cytotrophoblast ceases to function and fetal RBCs are lost into maternal circulation, this is called fetal-maternal hemorrhage (FMH). This antenatal mixing of fetal and maternal blood occurs frequently, even in asymptomatic women, and can lead to sensitization. (3) FMH is most common during labor, but can occur earlier in the pregnancy. As Emergency Physician’s we can help to prevent HDFN by recognizing fetal-maternal hemorrhage and other sensitizing events in Rh-negative women and subsequently providing Anti-D immunoglobulin.

RhoGAM and Fetal-Maternal Hemorrhage: When should I consider giving Anti-D immunoglobulin as an Emergency Physician?

  • Rh-negative women with potential first trimester loss (bleeding), including threatened abortion and incomplete abortion.
  • Rh-negative women with cases of ectopic pregnancy.
  • Rh-negative women with antepartum hemorrhage
  • Pregnant Rh-negative women in cases of blunt abdominal trauma.
  • Intrauterine Fetal Death in Rh-negative women
  • Following delivery in Rh-negative women with Rh-positive and weakly positive children.

Inadequate data exists to provide evidence based recommendations about first trimester spontaneous abortion. Consequences of alloimmunization are severe, therefore administration of Rh D immune globulin should be considered in these circumstances. (3)

Indirect Coombs Test: The “Screen” of the “Type and Screen”

This is the most accurate technique for detecting in-vitro antibodies in the patient’s serum, based on anti-human globulin (Coombs reagent), which should be routinely ordered at the first prenatal visit and at the 28 week visit. This is useful in cross-matching blood prior to transfusion, diagnosing immune mediated hemolytic anemia and antenatal testing.

A type and screen last only 72 hours in an Rh-negative pregnant patient. This is the safeguard against the new development of maternal antibodies.

A women with a positive Indirect Coombs Test after administration of Rh-D immunoglobin should continue to be offered Rh-D immunoglobin when indicated as the antibodies identified are likely passively acquired, particularly if the titer does not exceed 1:4. (7)

Kleihauer-Betke (KB) acid-elution test:

The KB test is dependent on the intrinsic acid-sensitive nature of adult hemoglobin when compared with fetal hemoglobin. When a maternal blood smear is exposed to acid and subsequently washed, adult hemoglobin is eluted while fetal hemoglobin remains. A percentage of fetal RBCs are identified, after counting a minimum of 2,000 RBCs, and used to calculate the volume of fetal-maternal hemorrhage (FMH).

(% of fetal cells determined by Kleihauer-Betke test/100) x 5,000 mL = volume of FMH (mLs)

The above equation, used to calculate FMH, assumes maternal volume to be 5,000 mL. This can result in both underestimations and overestimations, most of the studies report the tendency of the Kleihauer-Betke test to overestimate FMH. There are multiple published formulas available for the calculation of FMH which reflect different assumptions based on maternal blood volume, maternal hematocrit, fetal hematocrit, fetal MCV, effectiveness of staining non-eluted fetal hemoglobin (5).  The above formula is recommended by the American Association of Blood Banks' (AABB) Technical Manual. It should be noted that while there is controversy surrounding estimation of FMH through the KB test, 95% of laboratories testing for fetal RBC detection use this for fetal RBC quantification. (4)

Some Caveats

  • Many sources do not recommend FMH quantification (A.K.A. KB test) at < 20 weeks, as the fetoplacental blood volume is estimated to be 30 ml at 20 weeks and one vial (300 μg) of RhIg is sufficient to protect against 30 mL of fetal whole blood (or 15 mL of fetal RBCs). (3) At UC Health we choose to not perform KB tests < 16 weeks (3)
  • All Rh D-negative women giving birth to Rh D-positive infants undergo additional testing (KB test) for FMH quantification as screening only if their pregnancy is designated as high risk. (High risk: abruptio placentae, placenta previa, intrauterine manipulation, or fetal death) (3)
  • Kleihauer–Betke test may not be accurate in conditions where the mother has a coexistent medical condition associated with increased percentage of hemoglobin F in the RBC. These conditions include sickle cell disease, β-thalassemia, hereditary persistence of fetal hemoglobin (HPFH), acute stress erythropoiesis, and pregnancy. In 25% of pregnant women, HbF begins to increase at 8 weeks' gestation and peaks at 18–22 weeks, and may reach levels as high as 7% by 32 weeks. Alternative methods, such as flow cytometry should be used (6)
  • Routine Rh immunoprophylaxis (at 28 weeks gestation) is not discussed above

Content by Adam Gottula, MD

Peer Review by Ryan LaFollette, MD