The Rh antibody titer was studied during pregnancy and after delivery in 11 cases in which previously sensitized Rh-negative mothers had Rh-negative babies. In addition, 1 case was studied in which a type Rh1 mother, previously sensitized to the rh'' factor, gave birth to a type Rh1 baby. In all cases the babies were normal at birth and the baby’s serum contained univalent Rh antibodies equal in titer to those present in the maternal serum. In no case was there a rise in the antibody titer in the maternal serum either during the pregnancy or after the baby was born. Thus, it has not been possible to confirm claims concerning a "nonspecific anamnestic rise" in Rh antibody titer said to be caused by an Rh-negative baby.
Two illustrative cases are described in detail. In one of the cases described, there was no appreciable change in Rh antibody titer during the pregnancy despite the use of so-called Rh hapten; nor had there been an appreciable change in titer for as long as two and one-half years previously. The Rh antibody titer of the baby’s blood dropped about 98 per cent by the end of the sixth month, while during the same period of time the maternal antibody titer fell only approximately 35 per cent. Based on the course of the Rh antibody titer of the baby’s serum, the half-life of the antibody globulin molecule is estimated to be about thirty days.