Matching blood group before marriage is important. This is to prevent Rh incompatibility. Rh incompatibility can lead to erythroblastosis fetalis (Hemolytic disease of the newborn-HDN). Fetal RBC gets destroyed & newborn may get severe anaemia, jaundice. This jaundice is more severe than Physiological jaundice ( which is the most common and will usually resolve on its own).
In very severe form, a fetus may die due to heart failure. This is mediated by the antigen-antibodies reaction. Transfer of maternal antibodies across the placenta occurs. This happens when Rh +ve man marries Rh-ve lady.
So Rh +ve man should try to avoid marrying Rh-ve lady.
Matching blood groups for marriage ::
Boy : A = Girl:A & AB
Boy : B = Girl:B & AB
Boy : O = Girl:O, A, B & AB
Boy : AB = Girl : AB
Boy : Rh+ve = Girl : Rh+ve
Boy : Rh-ve = Girl : Rh+ve & Rh-ve.
Blood groups that do not match for marriage ::
Boy : A = Girl : O & B
Boy : B = Girl : O & A
Boy : AB = Girl : O, A & B
Boy : Rh+ve = Girl : Rh-ve.