Maternal red cells may cross the placental barrier and enter the fetal circulation, and this transfer may cause primary sensitization in Rh-negative girls born to Rh-positive mothers.
60 families were studied. Each family consisted of the grandmother, her Rh-negative daughter, and the Rh-positive grandchildren. Only families with ABO compatibility in the three generations, and where the mothers had never been transfused or had never received blood intramuscularly, were selected.
The families were divided into 2 groups: the group of the Rh-positive grandmothers, group (+), which consisted of 40 families, and the group of Rh-negative grandmothers, group (-), which consisted of 20 families.
The 2 groups were analysed as to the presence of affected grandchildren in any pregnancy. There were 35 (87·5%) affected grandchildren in group (+), and 15 (75%) affected children in group (-).
In group (+) the number of mothers with 3 or more Rh-positive pregnancies was 16, and of these, 4 (25%) had only unaffected children. In group (-) 15 mothers had 3 or more Rh-positive pregnancies, and of these, 4 (27%) had only unaffected children.
There was a striking similarity in the percentage of affected children between the 1st birth in group (+), 20%, and the 2nd birth in group (-), 20%; the 2nd birth in group (+), 38%, and the 3rd birth in group (-), 30%; the 3rd birth in group (+), 28%, and the 4th birth in group (-), 25%.
It was concluded that (1) an Rh-positive grandmother acts similarly to the antigenic stimulation caused by pregnancy and the birth of an Rh-positive fetus; (2) it might be advisable to inject all Rh-negative newborn females, born to Rh-positive mothers, with anti-D γ-globulin, soon after birth; (3) prediction of the risk of erythroblastosis, especially in the case of primigravidae or mothers with one non-affected Rh-positive child, requires the investigation of the blood group of the grandmother on the mother's side.
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