Blood Group Compatibility for intending couples.

                                                

It is advisable that intending couples should know their blood groups before marriage. The blood groups are designated by the letters O, A, B, AB. Blood groups have a hereditary basis and depend upon a series of alternative genes, a fact sometimes utilized in solving the problems of disputed parentage.
Equally important and linked to the blood group is the Rhesus antigen, which is positive in 83% of the British population but about 95% among the black population.
Thus one can be O Rhesus positive (O+ve) or O Rhesus negative (O-ve). When an Rh +ve blood is given to an Rh -ve person, then Rhesus antibodies are stimulated; for instance, immunization of a woman can result from blood transfusion or injection of Rh positive blood. In women, also, immunization due to pregnancy can result from the passage of the Rh +ve antigen from a Rh positive fetus across the placenta into the circulation of a Rh negative woman.
It must be emphasized that when an Rh-ve woman is married to an Rh positive man, the chance for her becoming sensitized to the Rh antigen and thus having children affected with haemolytic (red cell breakdown) disease of the new-born is relatively small. The risk of developing antibodies increases with succeeding pregnancies, thus if a Rh-ve woman marries a Rh +ve man, there is 1 in 143 chance of Rhesus iso-immunization during the first pregnancy, 1 in 14 during the 2nd and 3rd; 1 in 12 during the 4th, and 1 in 8 during the 5th pregnancy.
The overall incidence of haemolytic disease of the newborn due to this problem is about 1 in 200 of all pregnancies. Usually, sensitization due to pregnancy practically never results in haemolytic disease in the first child; on the other hand, sensitization due to previous blood transfusion may cause the first child to be affected. Thus the importance of avoiding the transfusion of Rh +ve blood to a Rh -ve person must be emphasized.
In conclusion, in view of the low risk of Rhesus iso-immunization, Rhesus factor does not constitute an absolute contraindication why a Rh -ve woman should not marry a Rh +ve man. Even in the few cases where sensitization occurs, the affected child can still be effectively treated. There is a drug that can be used to prevent sensitization if the Rhesus status of the couple is known initially. There is no risk of Rhesus iso-immunization if both couple are Rhesus +ve, or are Rhesus -ve, or if a Rh -ve man marries a Rh +ve woman.
I'll conclude this article with Dr. Peter's final advice on the matter...

Know your blood group and genotype.
Help in preventing genetic diseases by marrying a partner of compatible genotype.
Determine the Rhesus status of every newly-born child.
Consult your obstetrician during pregnancy.