Shoshy, I agree with you that the main problem is when the mother's and baby's blood come into contact with each other. Which under normal circumstances as you stated this does not happen. No matter what the blood type this will present a problem along with other things.
The RH factor can give an added problem with all the blood types. Mamma3, It would be very interesting to know what the RH neg. or RH pos. factors were of the persons you spoke about because it could make a big difference and further the danger.

A RH pos. mother and RH pos. baby is not a problem. A RH neg. mother and RH neg baby is not a problem. A RH pos. mother and RH neg baby is not a problem. However a RH neg. mother carrying a RH pos. child is a great danger especially if the mother has antibodies against the RH positive blood. The touching of the two blood types in this case, will kill the childs blood. Again normally the mother and baby's blood do not touch each other.

Homeopathy works by keeping the mothers tissues strong so there is no leakage in the placenta between mother and baby. The birth of the baby is also a critical time to not allow any blood contact of mother and child's blood. At this time the baby's blood touching the mothers could put antibodies in the mother's blood putting further pregnancies in danger even if the current one was not effected. In this case homeopathy is especially helpful to keep the connective tissue healthy.