Learn The BasicsThere are several tests available to diagnose hemolytic disease of the fetus and newborn (HDFN). Some of these tests can be done during pregnancy, while others are done after the baby is born.
Diagnostic tests before birth
The tests that can be used to diagnose HDFN before a baby is born include amniocentesis, ultrasound, and blood tests on the mother or the umbilical cord.
Blood tests
A blood test can be done on blood drawn from a pregnant woman to see whether she has antibodies against the red blood cells of her baby. If so, the red blood cell antigen status of the father should be evaluated to determine whether the baby may have inherited such antigens from their father. (An antigen is a substance that is able to stimulate an immune response).
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A blood test called a cordocentesis can also be done on a sample obtained from the umbilical cord of the baby to check for the presence of antibodies, bilirubin and anemia in the fetus. Bilirubin is the by-product of red blood cell breakdown and may be the result of the mother’s immune system attacking the baby’s red blood cells.
Amniocentesis
Amniocentesis is a medical procedure in which a small amount of amniotic fluid is extracted from the amniotic sac during pregnancy. This fluid contains fetal cells and can help determine the blood type of the fetus. It should be done if the mother has been determined to have alloimmunization or an immune response against red blood cells.
Ultrasound
An ultrasound can help determine the presence of organ enlargement in the fetus, which may occur as a result of fetal anemia.
Another type of ultrasound called a Doppler ultrasound, can be used to measure the peak systolic velocity of the middle cerebral artery in the brain of the fetus, which is also a sign of fetal anemia.
Diagnostic tests after birth
Blood tests can also be done once the baby is born to confirm HDFN.
Umbilical cord testing
The baby’s umbilical cord blood may be tested after birth to identify their blood group, Rh factor, red blood cell count and antibodies.
The American Academy of Pediatrics (AAP) states that in infants born at 35 weeks or more gestation who develop jaundice in the absence of maternal prenatal blood grouping or if the mother is Rh negative, a direct antibody test (or Coombs’ test), blood type and an Rh (D) type on the infant’s (cord) blood are strongly recommended.
Fetal blood testing
After birth, the baby’s blood can be tested for bilirubin levels, once again to check whether their red blood cells are being broken down.
Differential Diagnosis
HDFN is considered in cases where a newborn baby has jaundice or high levels of bilirubin and neonatal anemia. However, there may be other conditions that share similar signs or symptoms. The process of differentiating between two or more such conditions is called differential diagnosis.
The differential diagnosis of HDFN may include red blood cell enzyme disorders, hemoglobin synthesis disorders, red blood cell membrane abnormalities, hemangiomas or a usually benign vascular tumor derived from blood vessel cells, acquired conditions, such as sepsis and infections, and hemolysis or the destruction of red blood cells due to medications.
HDFN can be diagnosed for certain by identifying the presence of red blood cell antibodies in the blood of the mother and/or a positive direct antibody test in the serum of the baby.
Reviewed by Kyle Habet, MD, on September 7, 2023.
