Development of multiple antibodies in an apparently 'protected' Rh D negative mother

A case is described of a group O Rh (D) negative woman who received a blood transfusion after the delivery of her first infant, blood group O Rh (D) negative. In her second pregnancy anti-S was detected, presumably due to the prior transfusion. The second infant was D+S+ and the direct antiglobulin test on this infant's cells was positive. As no anti-D antibodies were detectable in this pregnancy, the positive antiglobulin test was presumably due to the anti-S. Anti-D immunoglobulin was administered after this pregnancy, but in spite of this the mother developed a strong anti-D antibody. The significance of this 'failure of protection' is discussed in relation to the augmenting affect of antibody development during pregnancy.