Isoimmunization
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Introduction
Isoimmunization is the production of antibodies against RBC antgens as a result of stimulation with other RBCs.
The risks of isoimmunization of an Rh -ve mother with an Rh +ve baby is 16%: 2% antepartum, 7% within six months of delivery (HOW?) and 7% with the second pregnancy.
The Case of Mabel Utingua
Mabel is a 34 year-old woman with pregnant with her second child when she develops vaginal bleeding ten weeks into her pregnancy. She knows her blood type is A negative. Why should she be concerned?
Causes and Risk Factors
Maternal sensitization can occur following:
- incompatible blood transfusions
- previous fetal-maternal hemorrhage (ie ectopic pregnancy, abortion)
- procedures (prenatal diagnosis, cerclage, D&C)
- sharing needles
- labour and delivery
- naturally occurring (ie Kell, Duffy)
Pathophysiology
The maternal-fetal circulations are normally separated by the placenta. However, sensitization can occur as described above.
IgM is the primary response, with IgG appearing 2 weeks to 6 months.
Antigens include:
- Rho
- blood type
week gestation12 16 20 28 40 |
blood volume (ml)3 19 35 90 500 |
Signs and Symptoms
- history
- physical exam
History
Inquire into past obstetrical history, including:
- deliveries
- threatened miscarriages
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Routine screening should be done at the first visit for blood group, Rh status, and antibodies. Titres <1:16 are considered benign, while >1:16 leads to amniocentesis for biliary pigment evaluation of hemolysis.
Rh = D; both mother and father should be tested. If both are negative, or both are positive, there is no need for prophylaxis.
Rh can also be measured as indeterminant; some mothers are prophylaxed; others are not. (antigens D, C, c, E, e)
The Kliehauer-Betke test can determine extent of hemorrhage, but is time-consuming as the slides are stained and airdried.
If antibody screen is positive, they should be screened for:
Cord blood
DAT
if positive: hemolytic disease;
Diagnostic Imaging
A fetal ultrasound can show fetal hydrops, or total body edema.
Doppler ultrasound of baby's arteries can show flow velocity. The higher the velocity, the greater the likelihood of hemorrhage and anemia.
Treatments
Prophylaxis
Rh IgG (RhoGam or WinRho) can be given to bind the Rh Ag of fetal cells and prevent maternal immune system activation. Unfortunately, once antibodies begun being produced, there is no benefit of Rh IgG.
Rhogam can be given routinely to all Rh -ve women in the following conditions:
- routinely at 28 weeks GA
- within 72h ouf birth
- with a positive Kliehauer-Betke test
- with any invasive procedure done during pregnancy
- in ectopic pregnancy
- with miscarriage or therapeutic abortion
- with antepartum hemorrhage
Treatment
Intrauterine transfusion of packed RBCs can be given if the fetus is severely affected.
Consequences and Course
Anti-Rh Ab leads to fetal hemolysis. Mild disease can resolve completely following birth. However, it can also cause fetal:
- anemia
- CHF
- edema and ascites
Severe hemolysis can lead to fetal hydrops or erythroblastosis fetalis.
Resources and References
Topic Development
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