An Rh-negative woman who conceives a child with an Rh-positive man is at risk for Rh incompatibility.
Rh factor is inherited (passed from parents to children through the genes). If you're Rh-negative and the father of your baby is Rh-positive, the baby has a 50 percent or more chance of having Rh-positive blood.
Simple blood tests can show whether you and the father of your baby are Rh-positive or Rh-negative.
If you're Rh-negative, your risk of problems from Rh incompatibility is higher if you were exposed to Rh-positive blood before the pregnancy. This may have happened during:
Certain tests also can expose you to Rh-positive blood. Examples include amniocentesis (AM-ne-o-sen-TE-sis) and chorionic villus (ko-re-ON-ik VIL-us) sampling (CVS).
Amniocentesis is a test that you may have during pregnancy. Your doctor uses a needle to remove a small amount of fluid from the sac around your baby. The fluid is then tested for various reasons.
CVS also may be done during pregnancy. For this test, your doctor threads a thin tube through the vagina and cervix to the placenta. He or she removes a tissue sample from the placenta using gentle suction. The tissue sample is tested for various reasons.
Unless you were treated with the medicine that prevents Rh antibodies (Rh immune globulin) after each of these events, you're at risk for Rh incompatibility during current and future pregnancies.