There is no need to match blood groups prior to marriage, but it is important to know the ABO & Rh blood group of the partners. This is so because in case a Rh negative female marries a Rh positive male, there is a possibility that the baby might be Rh positive. This situation can lead to Rh isoimmunisation, i.e. during development in the womb or child birth, if the baby's blood enters the mother, it will induce the production of antibodies in the mother as the baby's Rh positive blood is foreign to the Rh negative mother's immune system. These antibodies in the mother can then cross across the placenta and enter the baby's blood leading to a reaction that destroys the baby's Rh positive red blood cells leading to anaemia, jaundice, etc. In case the blood group is known in advance, the doctor takes due precaution during pregnancy to minimise the possibility of this reaction occurring.