To diagnose erythroblastosis fetalis, a doctor will order a routine blood test
during your first prenatal visit
. They’ll test for your blood type
. The test will also help them determine whether you have anti-Rh antibodies in your blood from a previous pregnancy. The fetus’s blood type is rarely tested. It’s difficult to test for a fetus’s blood type and doing so can increase the risk for complications.
Frequency of testing
If initial testing shows your baby may be at risk for erythroblastosis fetalis, your blood will be continually tested for antibodies throughout your pregnancy — approximately every two to four weeks. If your antibody levels start to rise, a doctor may recommend a test to detect fetal cerebral artery blood flow, which isn’t invasive to the baby. Erythroblastosis fetalis is suspected if the baby’s blood flow is affected.
If you have Rh-negative blood, the father’s blood will be tested. If the father’s blood type is Rh negative, no further testing is needed. However, if the father’s blood type is Rh positive or their blood type isn’t known, your blood may be tested again between 18
weeks of pregnancy, and again at 26
weeks. You’ll also receive treatment to prevent erythroblastosis fetalis.
If your baby is jaundiced
after birth, but Rh incompatibility isn’t a concern, the baby may be experiencing problems due to ABO incompatibility. ABO incompatibility occurs most frequently when a mother with an O blood type gives birth to a baby who has an A, B, or AB blood type. Because O blood types may produce both A and B antibodies, the mother’s blood can attack the baby’s. However, these symptoms are generally much milder than a Rh incompatibility. ABO incompatibility can be detected via a blood test known as a Coombs test
. This test, along with a test to determine the baby’s blood type, is performed after the baby is born. It can indicate why the baby may appear jaundiced or anemic. These tests are usually done for all babies whose mothers have type O blood.