Why Are Blood Types Important During Pregnancy?

To prevent problems from RhD mismatch, a treatment called RhD Immune Globulin (RhIG), also known as WinRho, will be recommended. RhIG is a blood product that helps stop your body from making anti-D antibodies against your baby’s RhD positive blood.

When you are pregnant, a health-care provider will order prenatal blood work to find out your blood type and check for antibodies. This is one of the routine blood tests done early in pregnancy. The best time to do this test is between 8 and 11 weeks of your pregnancy.

If you are RhD negative, and you do not have anti-D antibodies, a test called Fetal RHD screening is recommended to check your baby’s RhD blood type. This screening test is done early in pregnancy using a blood sample from you. 

Knowing your baby’s RhD blood type early in your pregnancy can help you and a health-care provider decide if you need RhIG treatment.  About 40% of RhD negative pregnant people are carrying a baby who is also RhD negative, so they don’t need RhIG treatment.

Antibodies are part of your immune system. They help protect you against anything your body sees as different. Most people do not have antibodies against other blood groups.

If you test positive for antibodies, it means your body has made red blood cell antibodies after being exposed to a different blood group. This can happen during pregnancy if your baby’s blood group is different from yours, or after a blood transfusion. This is called alloimmunization (or sensitization).  A health-care provider will check which antibodies you have and if they could affect your baby.

Not all antibodies cause problems during pregnancy, and not every pregnancy with alloimmunization will have complications.

Alloimmunization usually does not cause problems. But during pregnancy, some antibodies can pass into your baby’s blood through the placenta. If your baby’s blood group is one that your antibodies react to, the antibodies can break down your baby’s red blood cells.  This can lead to a condition called hemolytic disease of the fetus and newborn (also known as HDFN). Problems due to HDFN can happen before or after your baby is born, including:  Anemia (not enough red blood cells) Jaundice (too much bilirubin, which can turn the skin and eyes yellow) In rare cases, the baby may need a blood transfusion, before or after birth. The symptoms of HDFN can range from mild to severe. Not all babies will have symptoms. Most babies recover within a few weeks and have no lasting problems. Careful monitoring and treatment during pregnancy and after birth can prevent most serious problems.