Prevention of Rh D Alloimmunization

Question 1

Rh D

Answer 1

erythrocyte antigen

Question 2

Percentage of women who are Rh negative who will become alloimmunized; when does it usually occur?

Answer 2

17% for each pregnancy; during the third trimester

Question 3

First and second trimester causes of alloimmunization

Answer 3

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%

Question 4

When is anti-D immune globulin recommended for Rh negative women during pregnancy

Answer 4

28-29 weeks gestation (reduces rates of alloimmunization to 0.1%) routinely or prior to procedures with risk of fetomaternal hemorrhage

Question 5

Normal dose of anti-D immune globulin

Answer 5

single dose of 300micrograms, if delivery has not occured within 12 weeks from last dose a repeat dose is recommended

Question 6

Amount of fetomaternal hemorrhage covered by standard 300 microgram dose of ant-D immune globulin

Answer 6

30 mL of Rh positive blood or 15 mL of fetal cells

Question 7

When should Rh-negative mothers delivering Rh-positive infants be screened for fetomaternal hemorrhage in excess of that covered by the standard dose?

Answer 7

After delivery for all

Question 8

What percentage of Rh-negative mothers become alloimmunized? What are the reasons?

Answer 8

0. 1-0.2%
1. failure to implement standard prophylaxis protocols
2. Spontaneous immunization despite prophylaxis

Question 9

Preventable reasons for alloimmunization of Rh-negative women

Answer 9

1. Failure to administer an antenatal dose of anti-D immune globulin at 28-29 weeks of gestation
2. Failure to recognize clinical events that place patients at risk for alloimmunization and failure to administer anti-D immune globulin appropriately
3. 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

Question 10

Suggested ways of decreasing the potential shortage anti-D immune globulin

Answer 10

Limiting doses for first-trimester indications and using lower doses of Rh D immune globulin for antenatal prophylaxis

Question 11

Should anti-D immune globulin ever be withheld from a woman undergoing sterilization?

Answer 11

Patients should be able to select it if they want, but not routinely recommended

Question 12

How should one deal with the issue of paternity?

Answer 12

If the father is known to be Rh negative, prophylaxis is unnecessary.

Question 13

Is it necessary to repeat antibody screening in patients at 28 weeks of gestation prior to the administration of anti-D immune globulin?

Answer 13

Left to the judgment of the physician; considered due to possibility of alloimmunization prior to 28 weeks (only 0.18% occurrence).

Question 14

Is anti-D immune globulin indicated in a sensitized pregnancy?

Answer 14

No

Question 15

How should a D^u blood type be interpreted, and what management should be undertaken?

Answer 15

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.

Question 16

Is threatened abortion an indication for anti-D immune globulin prophylaxis?

Answer 16

No evidence-based recommendation can be made, but not commonly done at or before 12 weeks

Question 17

When does the Rh D antigen appear on fetal erythrocytes?

Answer 17

As early as 38 days

Question 18

How much anti-D immune globulin should be given for first-trimester events and procedures?

Answer 18

50 micrograms to protect against sensitization by 2.5mL of blood
- abortions occuring after the first-trimester should receive the standard 300 microgram dose

Question 19

Should anti-D immune globulin be given in cases of molar pregnancy?

Answer 19

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.

Question 20

Should anti-D immune globulin be given in cases of intrauterine fetal death occurring in the second or third trimester?

Answer 20

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.

Question 21

Is second or third trimester antenatal hemorrhage an indication for anti-D immune globulin prophylaxis?

Answer 21

Yes

Question 22

How do you manage a woman in her second or third trimester with a persistent or intermittent antenatal bleed?

Answer 22

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.

Question 23

Is anti-D immune globulin prophylaxis indicated after abdominal trauma in susceptible pregnant women?

Answer 23

Yes, with follow-up screening for excess bleeding

Question 24

What should be done if an Rh D negative patient is discharged without receiving anti-D immune globulin after a potentially sensitizing event?

Answer 24

They are still eligible for receiving it up to 28 days postpartum but its only proven to be beneficial 13 days after.

Question 25

How long does the effect of anti-D immune globulin last?

Answer 25

Half-life is 24 days

Question 26

How do you determine excessive fetomaternal hemorrhage?

Answer 26

Positive Kleihaur-Betke test or a negative indirect Coombs test

Question 27

Should administration of anti-D immune globulin be repeated in patients with a post-date pregnancy?

Answer 27

Left to physician’s judgement

- Thought to only last for 12 weeks

Question 28

Should all Rh-negative women be screened for excessive fetomaternal hemorrhage after delivery of an Rh positive infant?

Answer 28

Yes, not just high-risk events

Question 29

When should women receive a post-delivery dose of anti-D immune globulin?

Answer 29

Within 72 hours of delivery of an Rh positive infant