Red Cell Antibodies during Pregnancy, Flashcards
Prepregnancy counselling for Red cell antibodies
- If red cell antibodies,
- particularly if risk of fetal anaemia or
- if compatible donor red cells for transfusion may be difficult to obtain,
should attend for “prepregnancy counselling” with clinician with knowledge and expertise of this condition.
All women should have their blood group and antibody status determined at
- at booking and
- at 28 weeks of gestation
What are the implications for the fetus and neonate from red cell antibodies?
- severe fetal anaemia can result in hydrops
- which significantly worsens the perinatal outcome
When and how should paternal and fetal genotyping be performed?
For maternal RBC antibodies (D, C, c, E, e and K)
Non-invasive fetal genotyping (maternal blood) performed in first instance for relevant antigen
- For other antigens, invasive testing CVS or amniocentesis may be considered if fetal anaemia is a concern or if invasive testing is performed for another reason (e.g. karyotyping).
Is karyotyping contraindicated in the presence of maternal red cell antibodies?
- Invasive testing is not contraindicated if alloimmunisation has occurred.
- Anti-D prophylaxis should be given to cover invasive testing if the mother is rhesus D (RhD) negative and is not sensitised.
If the fetus is at risk of anaemia, when should referral to a fetal medicine specialist take place?
Referral to FM specialist,
1 - when rising antibody levels/ titres,
2 - level/titre above a specific threshold or
3 - ultrasound features suggestive of fetal anaemia.
4 - if history of unexplained severe neonatal jaundice, neonatal anaemia requiring transfusion or exchange transfusion, in order to exclude HDFN as cause.
For antibodies other than anti-D, anti-c and anti-K, the following should prompt referral to a fetal medicine
specialist:
1 - history of previous significant HDFN or IUT, or
2 - titre of 32 or above, especially if the titre is rising as rising titres correlate with increasing risk and severity of anaemia.
What thresholds should be used for the various antibodies that could cause fetal anaemia to trigger referral for further investigation or monitoring?
An anti-D level of > 4 iu/ml but < 15 iu/ml correlates with a moderate risk of HDFN and an anti-D level of > 15 iu/ml can cause severe HDFN. Referral for a fetal medicine opinion should therefore be made once anti-D levels are > 4 iu/ml.
An anti-c level of > 7.5 iu/ml but < 20 iu/ml correlates with a moderate risk of HDFN, whereas an antic level of > 20 iu/ml correlates with a high risk of HDFN. Referral for a fetal medicine opinion should therefore be made once anti-c levels are > 7.5 iu/ml.
For anti-K antibodies, referral should take place once detected, as severe fetal anaemia can occur even with low titres.
The presence of anti-E potentiates the severity of fetal anaemia due to anti-c antibodies so that referral at lower levels/titres is indicated (unless the fetus has only one of these antigens).
Once detected how often should antibody levels be monitored during pregnancy?
Anti-D and anti-c levels should be measured every 4 weeks up to 28 weeks of gestation and then every 2 weeks until delivery.
Although anti-K titres do not correlate well with either the development or severity of fetal anaemia, titres should nevertheless be measured every 4 weeks up to 28 weeks of gestation, then every 2 weeks until delivery.
For all other antibodies, retesting at 28 weeks is advised with the exception of women who have previous history of pregnancies affected with HDFN when early referral to a fetal medicine specialist is also recommended.
For antibodies that could potentially cause problems with cross-matching or issues with the availability of appropriate blood, discussion with the blood transfusion service is required regarding the frequency of antenatal testing. This may depend on the type of antibody as well as the likelihood of requiring blood at short notice.
How should pregnancies at risk of fetal anaemia be monitored?
The cause of the alloimmunisation, relevant past history and pregnancy outcomes should be ascertained in order to generate an assessment of risk of HDFN.
- If fetus carries corresponding antigen for maternal antibody which is capable of causing fetal anaemia and if antibody levels/titres rise beyond levels, then pregnancy should be monitored weekly by ultrasound, specifically assessing the fetal MCA PSV.
- Referral to FM specialist for consideration of invasive treatment should take place if MCA PSV rises above 1.5 multiples of median (MoM) threshold or if there are other signs of fetal anaemia.
- Fetal monitoring is required (as above) once anti-K is detected.
If fetal transfusion is required what type of donor blood should be used?
- Red cell preparations for IUT should be group O (low titre haemolysin) or ABO identical with fetus (if known) and negative for antigen(s) corresponding to maternal red cell antibodies.
- IUTs should be performed only in fetal medicine units that have requisite invasive skills and appropriate perinatal haematology expertise.
What blood or blood components can be administered in emergency to woman “known red cell antibodies”
- Decision to use ABO-, RhD- and K-compatible blood that is not matched for other antibodies VS O negative, where woman’s ABO and RhD groups are unknown, should be made on balance of risks (severe haemorrhage versus haemolytic transfusion reaction).
- Transfusion should not be delayed in event of life-threatening haemorrhage. Close liaison with transfusion laboratory is essential.
How often should pregnant women with red cell antibodies who are at high risk of requiring transfusion (placenta praevia, sickle cell disease etc.) be tested?
Pregnant women with red cell antibodies, who are assessed as being at high risk of requiring a blood
transfusion, should have a cross-match sample taken at least every week.
If maternal transfusion is required, what type of donor blood or blood components should be used?
Red cell components of
- same ABO group and
- same RhD type, and
- K negative &
- CMV negative, should be selected.
Should RhD-negative women who have anti-D or non-anti-D antibodies receive routine antenatal or postnatal
prophylaxis?
Anti-D immunoglobulin should be given to RhD-negative women with non-anti-D antibodies for routine antenatal prophylaxis, for potential antenatal sensitising events and postnatal prophylaxis.
If immune anti-D is detected, prophylaxis is no longer necessary.
Discussion and liaison with the transfusion laboratory are essential in determining whether anti-D antibodies are immune or passive in women who have previously received anti-D prophylaxis.
What are the long-term health concerns for the children of women with red cell antibodies during pregnancy?
- some infants may experience anaemia persisting for a few weeks following birth.
- some infants may develop late anaemia which is usually due to hyporegenerative anaemia.
