Background: Maternal antibodies to high incidence antigens pose a challenge for the management of mothers, in the event of haemorrhage, and their babies, with a risk of haemolytic disease of the foetus and newborn (HDFN).
Case: A 44 year-old G5P4 Zimbabwean woman was found to have anti-U antibodies during her 4th pregnancy, which ended in miscarriage at 6 weeks. Her 5th pregnancy was complicated by insulin requiring gestational diabetes, but there were normal foetal ultrasounds throughout. Anti-U titres were monitored, rising from 1:2 to 1:1024 at 36 weeks. Her only sibling was positive for the U antigen. Iron was optimised during pregnancy. She delivered a male child after induction of labour at 39 weeks gestation, weighing 2605g with Apgar scores of 9 and 9 at 1 and 5 minutes, respectively. The infant’s phenotype was O R0r (Dce,ce) K- M-N+S-s+, direct antiglobulin test was strongly positive, with a pan-agglutinating eluate. Haemolysis was confirmed by haemoglobin falling from 137g/L at 6 hours to 76g/L at 3 days, absent haptoglobin with the bilirubin rising to 310 µmol/L despite phototherapy and 3 doses of intravenous immunoglobulin (1g/kg). The Red Cross Blood Service had 2 units of frozen U negative available within Australia, one of which was transfused (30ml/kg). A unit of maternal blood was obtained, but never transfused. Two further fresh units of U negative blood were sourced from the UK, and later frozen. The baby improved and was discharged at 8 days of age.
Discussion: The U antigen is part of the MNS blood group system and has been implicated in haemolytic transfusion reaction and HDFN. The prevalence of U-negative individuals is between 0.2-1.7% of African blood donors. Antibodies to rare antigens may pose a risk for HDFN and the inability to source red cells for transfusion. A plan to manage transfusion should be considered early and pre-emptive cryopreservation considered in women with known rare antibodies.