Anti‐D Concentration in Mother and Child in Haemolytic Disease of the Newborn

. The relationship between the maternal anti‐D concentration measured in μg/ml at full term, the amount of anti‐D in the baby and the severity of haemolytic disease of the newborn was studied in 18 mother‐infant pairs. The amount of anti‐D in the baby varies between 2 and 30% of that in the mother and it is concluded that the rate of active transfer of anti‐D across the placenta is the rate limiting step in the reaction between anti‐D and foetal red cells. It is suggested that there is variation in the rate of placental transfer between individual mothers and that this is a factor in determining the severity of the disease. The results also suggest that measurement of maternal antibody in μg/ml rather than antiglobulin titre will not improve the accuracy of ante‐natal assessment of severity of the disease.