Prevention of Rh D Alloimmunization Flashcards
Rh D
erythrocyte antigen
Percentage of women who are Rh negative who will become alloimmunized; when does it usually occur?
17% for each pregnancy; during the third trimester
First and second trimester causes of alloimmunization
therapeutic abortion: 4-5% spontaneous abortion: 1.5-2% ectopic pregnancy threatened abortion: very small chance CVS: 14% amniocentesis: 7-15% even if the placenta isn't traversed cordocentesis and other percutaneous fetal procedures external cephalic version: 2-6%
When is anti-D immune globulin recommended for Rh negative women during pregnancy
28-29 weeks gestation (reduces rates of alloimmunization to 0.1%) routinely or prior to procedures with risk of fetomaternal hemorrhage
Normal dose of anti-D immune globulin
single dose of 300micrograms, if delivery has not occured within 12 weeks from last dose a repeat dose is recommended
Amount of fetomaternal hemorrhage covered by standard 300 microgram dose of ant-D immune globulin
30 mL of Rh positive blood or 15 mL of fetal cells
When should Rh-negative mothers delivering Rh-positive infants be screened for fetomaternal hemorrhage in excess of that covered by the standard dose?
After delivery for all
What percentage of Rh-negative mothers become alloimmunized? What are the reasons?
- 1-0.2%
- failure to implement standard prophylaxis protocols
- Spontaneous immunization despite prophylaxis
Preventable reasons for alloimmunization of Rh-negative women
- Failure to administer an antenatal dose of anti-D immune globulin at 28-29 weeks of gestation
- Failure to recognize clinical events that place patients at risk for alloimmunization and failure to administer anti-D immune globulin appropriately
- Failure to administer or failure to administer timely anti-D immune globulin postnatally to women who have given birth to an Rh-positive or untyped fetus
Suggested ways of decreasing the potential shortage anti-D immune globulin
Limiting doses for first-trimester indications and using lower doses of Rh D immune globulin for antenatal prophylaxis
Should anti-D immune globulin ever be withheld from a woman undergoing sterilization?
Patients should be able to select it if they want, but not routinely recommended
How should one deal with the issue of paternity?
If the father is known to be Rh negative, prophylaxis is unnecessary.
Is it necessary to repeat antibody screening in patients at 28 weeks of gestation prior to the administration of anti-D immune globulin?
Left to the judgment of the physician; considered due to possibility of alloimmunization prior to 28 weeks (only 0.18% occurrence).
Is anti-D immune globulin indicated in a sensitized pregnancy?
No
How should a D^u blood type be interpreted, and what management should be undertaken?
Aka weak D positive; considered Rh D positive and shouldn’t receive prophylaxis
- Only exception is in a woman whose pre-delivery Rh status is unknown and whose postpartum status shows D^u. In this case give anti D immune globulin and investigate for fetomaternal hemorrhage.
Is threatened abortion an indication for anti-D immune globulin prophylaxis?
No evidence-based recommendation can be made, but not commonly done at or before 12 weeks
When does the Rh D antigen appear on fetal erythrocytes?
As early as 38 days
How much anti-D immune globulin should be given for first-trimester events and procedures?
50 micrograms to protect against sensitization by 2.5mL of blood
- abortions occuring after the first-trimester should receive the standard 300 microgram dose
Should anti-D immune globulin be given in cases of molar pregnancy?
Yes
- Theoretically complete molar pregnancies wouldn’t need it because there is no organogenesis, but partial moles would, but since the differentiation is based on pathology, we give it to all.
Should anti-D immune globulin be given in cases of intrauterine fetal death occurring in the second or third trimester?
Yes and all should be screened for hemorrhage in excess of that covered by the standard dose.
- Fetal death is due to fetomaternal hemorrhage in 11-13% of cases with no obvious cause.
Is second or third trimester antenatal hemorrhage an indication for anti-D immune globulin prophylaxis?
Yes
How do you manage a woman in her second or third trimester with a persistent or intermittent antenatal bleed?
Commonly, serial indirect Coombs testing is done every 3 weeks to monitor. Positive result indicates the presence of anti-D immune globulin and negative result indicates that fetomaternal hemorrhage may have occurred and a Kleihaur-Betke test should be done.
Is anti-D immune globulin prophylaxis indicated after abdominal trauma in susceptible pregnant women?
Yes, with follow-up screening for excess bleeding
What should be done if an Rh D negative patient is discharged without receiving anti-D immune globulin after a potentially sensitizing event?
They are still eligible for receiving it up to 28 days postpartum but its only proven to be beneficial 13 days after.
How long does the effect of anti-D immune globulin last?
Half-life is 24 days
How do you determine excessive fetomaternal hemorrhage?
Positive Kleihaur-Betke test or a negative indirect Coombs test
Should administration of anti-D immune globulin be repeated in patients with a post-date pregnancy?
Left to physician’s judgement
- Thought to only last for 12 weeks
Should all Rh-negative women be screened for excessive fetomaternal hemorrhage after delivery of an Rh positive infant?
Yes, not just high-risk events
When should women receive a post-delivery dose of anti-D immune globulin?
Within 72 hours of delivery of an Rh positive infant
