Quantification of anti-c in haemolytic disease of the newborn.

Anti-c is an important Rh antibody that causes haemolytic disease of the newborn (HDN). We have carried out a retrospective analysis of the clinical outcome of pregnancy in 120 mothers with anti-c. Of these, 100 gave birth to c-positive infants, of whom 14 had severe HDN requiring exchange transfusion. In all of these, the maternal level was 9.5 iu/ml or greater. Of the 29 women with anti-c levels of 9.5 iu/ml or above, in addition to the 14 with severely affected infants, 15 had infants requiring only phototherapy or no treatment. Our observations suggest that when the anti-c level is below 7.5 iu/ml, the fetus is unlikely to be seriously affected and invasive obstetric intervention is unnecessary. Of the 120 women studied, 50% had had a blood transfusion, in most cases for obstetric complications in a previous pregnancy. Although it was not possible to attribute alloimmunization to blood transfusion rather than previous pregnancy in any individual case, this observation points to the value of routine c typing as part of antenatal screening, so that c-negative blood can be selected.