If the blood of a pregnant woman is rhesus-negative (Rh-negative) and the blood of the fetus is rhesus-positive (Rh-positive), the woman may develop antibodies, which can cause severe harm to subsequent children in particular. In order to prevent this effect called sensitization, all Rh-negative pregnant women in Germany currently receive a prophylaxis.
A new type of test using a blood sample of the pregnant woman can determine the child's rhesus factor already before birth, however. Provided the test is sufficiently reliable, many women might not need the prophylaxis. Currently, the blood of the newborn baby is tested directly after birth.