GTG 65 The Management of Women with Red Cell Antibodies during Pregnancy

Question 1

Which antigens can be identified by non-invasive fetal genotyping using maternal blood?

Answer 1

D, C, c, E, e and K antigens

For other antigens, invasive testing (chorionic villus sampling [CVS] or amniocentesis) may be considered
if fetal anaemia is a concern or if invasive testing is performed for another reason (e.g. karyotyping).

Question 2

At what level of anti-D should prompt referral to fetal medicine?

Answer 2

> 4 iu/mL; 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.

Question 3

At what level of anti-c should prompt referral to fetal medicine?

Answer 3

> 7.5 iu/mL

An anti-c level of > 7.5 iu/ml but < 20 iu/ml correlates with a moderate risk of HDFN, whereas an anti-
c 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.

Question 4

At what level of anti-K should prompt referral to fetal medicine?

Answer 4

Any level, For anti-K antibodies, referral should take place once detected, as severe fetal anaemia can occur even with low titres.

Question 5

Once detected how often should antibody levels be monitored during pregnancy?

Answer 5

Anti-D, anti-c levels, anti - K - every 4 weeks up to 28 weeks of gestation and then every
2 weeks until delivery.

For all other antibodies, retesting at 28 weeks is advised with the exception of women who have a previous history of pregnancies affected with HDFN when early referral to a fetal medicine specialist is
also recommended.

Question 6

If the fetus carries the corresponding antigen for a maternal antibody which is capable of causing fetal anaemia and if the antibody levels/titres rise beyond the levels, how should the pregnancy be monitored?

Answer 6

weekly by ultrasound- to assess the fetal middle cerebral artery peak systolic velocities (MCA PSV); if MCA PSV >1.5 MoM/ signs of fetal anaemia- refer to FMU for invasive tx

Question 7

If fetal transfusion is required what type of donor blood should be used?

Answer 7

group O (low titre haemolysin) or ABO identical with the fetus (if known) and negative for the antigen(s) corresponding to maternal red cell antibodies; plasma is removed by the blood centre to increase the haematocrit to
0.70–0.85 and it is always irradiated.