One third of very weakly Rh-immunized women show no increase in their level of Rh immunization during pregnancy and after delivery. Administration of 300 pg of Rh immune globulin at 6-week intervals does not alter the incidence of lack of progression of Rh immunization in such women. Thirty-three Rh-positive women who ultimately delivered ABO-compatible babies, had Kleihauer fetal transplacental hemorrhage (TPH) screening tests carried out at 2-week intervals during pregnancy and shortly after delivery. One third of the 33 women had no detectable TPH (8) or a TPH of 0.01 ml of fetal red cells (3). We conclude that one third of weakly Rh-immunized women failed to show any progression of their Rh immune response during pregnancy or after delivery because they were exposed to too few fetal red cells (0.01 ml or less) to produce such a response.

No abstract

Fetal blood sampling under ultrasound guidance has added a new dimension to the management of Rh hemolytic disease. Combined with the established parameters of history, antibody measurement and amniotic fluid ΔOD(450) readings, direct testing of the blood of the fetus completes the picture. As well as giving information that may be applied to decisions regarding management, an opportunity is provided to observe the mechanism of anti-D IgG-induced red cell destruction in vivo.