Ignoring or “not doing” premarital health counseling is one of the most likely causes of marital breakdown, causing many problems. What you need to know in advance are the blood groups (A, B, AB, O) and “rhesus” (+, -). Inherited diseases, which may have run in the family, should also be identified. You also need to know: eye health, diabetes and blood pressure... It's a good idea to take the STD or sexually transmitted disease test.