Maternal isoimmunisation

Specialty: Obstetrics
Age group: All

Criteria for referral to level 6 public hospital maternity service

• Previously affected baby
• Abnormal ultrasound finding:
  • high fetal middle cerebral arterial (MCA) peak systolic velocity (PSV) with greater than 1.5 multiple of median (MoMs)
  • fetal hydrops
• Antibody titre greater than or equal to 1:32 of any intermediate or high-risk antibody
• Any positive anti-K antibody.

Information to be included in the referral

Information that must be provided

• Previous baby's medical history
• Current and previous obstetric history
• Any history of previous sensitising event e.g. blood transfusion
• Blood group and antibody titres
• Ultrasound reports.

Provide if available

• Not applicable.

Additional comments

The Summary and referral information lists the information that should be included in a referral request.

Referral to a level 6 maternity service should be considered in the context of the local maternity service system. Referring clinicians should contact the closest level 5 maternity service to discuss options.

'High risk' antibodies

• Anti-D isoimmunisation - A person who is identified as being Rhesus isoimmunised should not be given RhD-lg injections at any stage during their pregnancy, as it will not benefit them or their baby. It is important to ensure that an immune antibody is not misinterpreted as residual RhD-lg. It is not possible to serologically differentiate passively acquired anti-D (due to RhD-lg) and immune anti-D, and RhD-lg prophylaxis should continue unless it is unequivocally confirmed that the anti-D is alloimmune.
• Anti-c - Haemolytic effect is similar to that of Anti-D.
• Anti-K (or other Kell blood group system antibodies such as k, Kpa, Kpb) are all high-risk antibodies. Anti-K impairs haematopoiesis as well as causing haemolysis and peripheral sequestration. Previous obstetric history is not predictive of the likely severity of disease related to anti-K antibodies. Also, anti-K titres do not correlate with clinical severity.

'Intermediate risk' antibodies

• Other than anti-D, anti-c and anti-K, antibodies that may be of clinical significance include M, Rh other than D and c (such as C, E, e), S, s, U, Lutheran, Duffy (Fya, Fyb), Kidd (Jka, Jkb), H, Diego (Dia, Dib), Scianna, Colton, Gerbich and Vel. These are defined as intermediate risk antibodies.

If intermediate risk antibodies are detected during routine pregnancy testing, either at the initial visit or at 28 weeks gestation, a titration should be performed. If the titre is greater than or equal to 32, the person should be referred to a level 6 maternity service for assessment of potential fetal anaemia by MCA Doppler and to develop ongoing management plans.

'Low risk' antibodies

In general, these antibodies do not cause HDFN, and pregnancies affected by them can be managed as usual. These include Lewis (Lea, Leb), HLA/Bg, N, P1, Yt, Xg, Dombrock, LW, Chido/Rogers, Cromer, Knops, Indian, JMH, I and HI.

Referral to a level 6 public hospital maternity service is not appropriate for

• Low risk positive antibody result.