Rh Negative Blood and Pregnancy

At your first prenatal visit, a blood sample will be drawn to assess your blood type and Rh factor. Blood types are A, B, AB and O.  The Rh (Rhesus) factor is an inherited trait that refers to a specific protein located on the surface of the red blood cells. Those who have the protein are Rh positive; without it, Rh negative.  The large majority of people are Rh positive.  It does not affect your health in any way, but it becomes important while you are pregnant.

During pregnancy, or even more likely, during delivery, there may be some of the baby’s red blood cells that mix with your blood. If you are Rh positive, there is no problem. However, if you are Rh negative and the baby’s blood is Rh positive, your body may build up antibodies after exposure to the baby’s red blood cells.  This usually does not affect the first pregnancy. However, there is a possibility with subsequent pregnancies that if your baby is RH positive, your antibodies may cross the placenta and attack the baby’s red blood cells.  This can cause Rh disease, which can include anemia and other potentially life threatening effects on the fetus.

If you are Rh negative, you have an option to test the blood of the baby’s father. If he is also Rh negative, then your baby will be Rh negative also. You then do not need to receive RhoGam®. However, if he is Rh positive (or not available to have blood drawn), and you are Rh negative, we will draw your blood again around 28 weeks of gestation to check for antibodies in your blood. If there are none, you will receive an injection of Rhesus immunoglobulin (commonly known as RhoGam®) to prevent antibody development during the remainder of your pregnancy. Common side effects include soreness at the injection site or a slight fever.  There are no harmful effects to the baby.  RhoGam® does not contain preservatives such as mercury or thimerisol.

If your baby is Rh positive, you will receive another injection at the hospital after your delivery; if the baby is Rh negative, no further medication is needed.

If you are Rh negative, there are other occasions when a dose of RhoGam® may be needed. These include miscarriage, ectopic pregnancy, chorionic villi sampling (CVS), amniocentesis, or bleeding during pregnancy.

RhoGam® is administered at Morristown Medical Center. Your midwife will give you instructions on taking your prescription there to obtain your injection. Ask your midwife if you have any other questions about your Rh negative status.