Summary:
The passage of incompatible maternal anti‐A and anti‐B isoagglutinins across the placenta can cause haemolysis of foetal erythrocytes. This occurs almost entirely in group A or B infants born to a group O mother, but only one in five such infants shows evidence of a mild haemolytic disease. This suggests that there must be factors protecting the foetal red cells against incompatible maternal antibody. The investigation described here suggests that one such factor is the presence of blood group substances in foetal serum.
In an investigation of the amount of A‐substance present in the cord blood of group A infants, significantly greater amounts were found in secretors than in non‐secretors. Also, in group A secretor infants, the amounts of A substance in the cord blood of infants with group O mothers was diminished in comparison with those with group A mothers. These findings are compatible with the idea that some of the A‐substance in the serum of the group A infants with O mothers had combined with maternal anti‐A agglutinin and had been removed from the circulation. This supports the suggestion that blood group substances in cord serum protect the foetal erythrocytes from incompatible maternal antibodies.