The Rh factor naturally exists on some people’s red blood cells. If your blood type is fol­lowed by “ + ,” you are “Rh positive,” and if not, you are “Rh negative.” This is impor­tant when you are having a blood transfusion or when pregnant.

A father who is Rh positive often passes on his blood type to the baby. If the baby’s mother is Rh negative, any of the fetal blood that comes into contact with hers (which happens during delivery, not pregnancy) will cause her to begin to manufacture anti­bodies against the fetal blood. This may be very dangerous for any future pregnancies. Because the mother has made antibodies to Rh-positive blood, she will reject the fetal Rh-positive blood, which can lead to fetal death. After an Rh-negative woman has de­livered, she is given Rhogam (row-GAM), which prevents antibodies from forming and ensures that her future pregnancies will be healthy. Rhogam is also given if an Rh-neg­ative pregnant woman has an amniocentesis, miscarriage, or abortion.