The Rh blood group system is one of the most important blood group systems for humans, along with the ABO system. However, in Vietnam, 99.96% of people belong to the Rh+ blood group and only 0.04-0.07% of people belong to the Rh-negative blood group. Therefore, people with Rh-negative blood group are rare and need to be careful in blood transfusion and obstetrics.