ABO haemolytic disease of the newborn.

The charts of newborn infants with positive direct Coombs' test were studied. Only cases in which the mother's blood was group O and the infant's group A or group B were studied. There was no difference between group A and group B infants in the frequency and severity of the hemolytic process caused by maternal antibodies. In group B infants, monospecific antibodies (anti-B) were associated with more severe hemolytic process than cross-reacting antibodies (anti-A,B). In group A infants there was no difference in the severity of the disease between monospecific antibodies (anti-A) and cross reacting antibodies (anti-A,B). Even though there was no significant difference in the sex distribution of affected infants, there was a higher number of boys in the more severely affected group.