Your Guide to Prenatal Tests

Blood Type & Rh/Antibody Screen  

Who: All women

When: At your first prenatal visit (generally six to ten weeks into your pregnancy)

How: A blood test

Why: To determine your blood type and Rh status. Your baby’s pediatrician will eventually need this information, because if you have type “O” blood and deliver a baby with “A” or “B” blood type, he may be at greater risk for jaundice. It’s also helpful data for your healthcare provider, in case you have complications during labor and need a transfusion. Secondly, the Rh factor is a protein found on red blood cells. If you are Rh-negative (meaning that you don’t have the protein) and your fetus is Rh-positive, your body may produce antibodies that attack your baby's red blood cells, potentially causing him to develop severe anemia in utero.

Results & follow-up: If an Rh difference is detected, a doctor can provide injections of Rh immune globulin to prevent this type of reaction (usually at 28 weeks gestation and within 72 hours of giving birth, although a dose may also be given if a woman has a miscarriage, bleeding, or an amniocentesis or other invasive testing during pregnancy).