Maternal D alloimmunization (prevention): Clinical sciences

Chapters:

Watch video only

Introduction0:00–0:46

Maternal D alloimmunization, sometimes called isoimmunization, occurs when a pregnant patient with Rh-negative blood type is exposed to Rh-positive blood and develops antibodies against the Rh-factor antigen.
Maternal sensitization can occur when the fetus is Rh-positive, either during pregnancy, or during delivery, which is when fetal-maternal hemorrhage is most likely to occur.
Then, in subsequent pregnancies with an Rh-positive fetus, maternal anti-D antibodies can cross the placenta and attack the fetus’ red blood cells, causing fetal anemia.
Severe cases can result in fetal hydrops and death. Your first step when evaluating a pregnant patient who is Rh negative is to obtain a focused history.

Focused history0:46–2:27

The initial prenatal visit is an ideal opportunity to evaluate a patient’s risk and provide education about sensitization.
Additionally, the 28-week visit is the recommended time to administer anti-D immune globulin for routine prophylaxis. Keep in mind that maternal D alloimmunization can occur in asymptomatic patients who don’t receive immune globulin prophylaxis at 28 weeks, because some antenatal mixing of fetal and maternal blood occurs despite the separate circulations.
Alright, other important findings include vaginal bleeding, or other sensitizing events in pregnancy that could have caused maternal exposure to fetal red blood cells, such as abdominal trauma, chorionic villus sampling, amniocentesis, cordocentesis, and external cephalic version.
Additionally, spontaneous abortion, ectopic pregnancy, and pregnancy-related uterine curettage can also cause maternal exposure.
Ask patients who are known to be Rh-negative if they have received immune globulin in the past 12 weeks, because this could result in a positive antibody screen.
Knowing the paternal blood type can also be helpful because Rh-negative patients are not at risk of Rh D alloimmunization when paternity is certain and paternal blood type is Rh-negative.
Finally, gestational age is important because it influences the minimum dose of anti-D immune globulin required when antepartum bleeding or another sensitizing event occurs.
Your next step is to obtain an ABO and RhD blood type and antibody screen. This is a routine blood test for all patients at the initial prenatal visit, and upon admission for labor and delivery.

ABO/RhD blood type2:27–3:27

For Rh-negative patients, the antibody screen is also repeated at 28 weeks of pregnancy. However, if a patient is at risk for sensitization at other times during gestation, repeat the antibody screen if the patient is Rh-negative, or if their blood type is unknown.
Of note, this should be done before anti-D globulin is administered, otherwise that could cause false-positive results.Most patients who are Rh D negative will have a negative anti-D antibody screen.
Your next step for these patients is to assess for vaginal bleeding or another sensitizing event. If a sensitizing event has occurred, manage the patient according to obstetrical guidelines, and administer anti-D globulin.Ok, now, delivery is a high-risk event for Rh D alloimmunization in Rh negative individuals.

Delivery3:27–4:43

Within the first 72 hours postpartum, determine the Rh D status of the infant. If the infant is Rh-negative, no further treatment is necessary.
If the infant is Rh-positive, your next step is to assess for fetal-maternal hemorrhage. Screening for fetal-maternal hemorrhage begins with the erythrocyte rosette screen, which can detect a volume of fetal blood greater than 2 milliliters in the maternal circulation.
If the rosette screen is negative, administer the routine 300-microgram dose of immune globulin. However, if the screen is positive, quantify the amount of fetal-maternal hemorrhage with either a Kleihauer-Betke test or flow cytometry.
If a hemorrhage larger than 30 milliliters of fetal whole blood, or 15 milliliters of fetal red blood cells has occurred, additional vials of anti-D immune globulin should be given.
Here’s a high-yield fact! A 300-microgram dose of anti-D immune globulin is sufficient for a hemorrhage of up to 30 milliliters of fetal whole blood or 15 milliliters of fetal red blood cells.
The next group of potentially sensitizing events includes fetal demise or maternal abdominal trauma in the second or third trimesters and persistent antenatal bleeding.

Second/third trimester demise4:43–5:17

If any of these events occur, determine the volume of fetal-maternal hemorrhage with a Kleihauer-Betke test or flow cytometry, and administer the appropriate amount of anti-D immune globulin.
If pregnancy continues, re-evaluate the patient at 28 weeks and after delivery for routine prophylaxis as indicated. For all other sensitizing events, or if vaginal bleeding has occurred during pregnancy even in the absence of a sensitizing event, assess the gestational age to determine your next steps.

Other sensitizing events + vaginal bleeding5:17–6:26

Patients who are less than 13 weeks should receive a 50-microgram dose of anti-D immune globulin due to the smaller fetal blood volume at this gestation.
If the 50-microgram dose is unavailable, administer the 300-microgram dose. If the pregnancy continues, re-evaluate the patient at 28 weeks and after delivery for routine prophylaxis.
Patients at 13 weeks of gestation or greater should receive a 300-microgram dose of immune globulin. Reassess the patient at 28 weeks and after delivery for routine prophylaxis.
Here’s a high yield fact! If delivery, or a sensitizing event, such as third trimester bleeding, occurs within 3 weeks of antenatal anti-D globulin administration, administration of anti-D globulin after birth can be omitted if there hasn’t been excessive maternal-fetal hemorrhage during delivery!
The last scenario for pregnant patients who are Rh-negative with a negative antibody screen includes individuals who present in the absence of a sensitizing event or vaginal bleeding.

Bleeding/event absent6:26–7:32

You may see these patients at any time during their pregnancy, and they should be educated about their Rh-negative status, the risk of alloimmunization during pregnancy, and the recommendation for prophylaxis with anti-D immune globulin at 28 weeks, and postpartum if indicated.
Next, assess the patient’s gestational age. If the pregnancy is less than 28 weeks, reassure the patient and re-evaluate at 28 weeks and postpartum for routine prophylaxis.
If the pregnancy is 28 weeks or greater and the patient has not yet received the recommended 28-week prophylactic dose of immune globulin, repeat the anti-D antibody screen, and if negative, administer 300 micrograms of anti-D immune globulin.
Reevaluate after delivery for additional routine prophylaxis. Now let’s talk about Rh-negative pregnant patients who have a positive screen for anti-D antibodies.

RhD negative, antibody positive7:32–8:19

Your first step is to inquire about the patient’s last dose of anti-D immune globulin. If a dose was administered within the last 12 weeks, the positive antibody screen is most likely due to anti-D antibodies from the immune globulin.
Reassure these patients and consider the need for additional anti-D immune globulin if bleeding or another sensitizing event is present.
You should also re-evaluate at 28 weeks and postpartum for routine prophylaxis. However, if a dose of anti-D immune globulin has not been given in the past 12 weeks, you should suspect maternal D alloimmunization.
Alright, now, on the other hand, some patients can be weak-D positive. This means they either express reduced numbers of normal Rh D antigens, or partial or abnormal Rh D antigens.

Weak-D8:19–9:11

In the latter group, it’s possible to develop antibodies against the segment of the RhD antigen they are missing, leading to alloimmunization.
You should treat pregnant patients who are weak-D positive as having an Rh-negative blood type and administer anti-D immune globulin as indicated.
Here’s another clinical pearl! If an Rh-negative patient delivers an infant that is weak-D positive, the infant should be treated as Rh-positive.
Therefore, administer Rh immune globulin, because the Rh antigens from the infant could elicit sensitization in the mom.The final patients to consider have a blood type that is Rh D positive.

Rh positive9:11–9:26

These patients carry the D antigen on their red blood cells, and will not develop maternal D alloimmunization. Alright, as a quick recap… Prevention of maternal D alloimmunization avoids the development of maternal anti-D antibodies that can cross the placenta and destroy fetal red blood cells.

Review9:26–10:18

When assessing a patient for prevention of maternal D alloimmunization, start with a focused history for vaginal bleeding or other sensitizing events, recent administration of anti-D immune globulin, and gestational age.
Next, obtain an ABO and Rh D blood type and antibody screen. Manage Rh-negative patients based on whether vaginal bleeding or a sensitizing event has occurred and if anti-D antibodies are present.
In the absence of Rh D alloimmunization, administer an appropriate amount of anti-D immune globulin, including prophylaxis at 28 weeks and postpartum as indicated.