Hemolytic Disease of the Fetus and Newborn Diagnosis
Hemolytic disease of the fetus and newborn (HDFN), often called erythroblastosis fetalis, is a blood disorder that occurs when the blood types of a mother and baby are incompatible. For reference, “Hemolytic” means breaking down of the red blood cells and “Erythroblastosis” refers to the making of immature red blood cells.
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How is Hemolytic Disease of the Fetus and Newborn Diagnosed?
Checking the Father’s Blood Type
One of the first steps in determining if your unborn baby may be affected by your antibodies is to check the blood type of the baby’s father. In cases of Rhesus disease, the father of your unborn baby will be Rh negative (like your blood type) in 13 out of 100 cases. This will result in the baby not being affected at all. In other cases, the baby has a chance of being Rh positive (a different blood type from you). In these cases, the baby may develop a low blood count (anemia) while in the womb. If the father of the baby is Rh- positive, there is approximately a 1 in 2 chance that his blood type is of a mixed variety (heterozygous). This means that half of this offspring will be Rh negative (will have no problems) and the other half will be Rh positive (may develop anemia). This occurs by chance, like a roll of the dice, at the time of fertilization of the egg. If the father of the baby is found to be a pure Rh-positive blood type (homozygous), then all of his children will be Rh positive and have the chance to be affected by your antibodies. In cases of Rh disease, a partner can be tested through a special DNA blood test performed at a special laboratory. In the case of red cell alloimmunization due to other red cell antigens, a partner can be tested to see if he is heterozygous or homozygous through a simple blood test performed at most hospital blood banks.
Free Fetal DNA
If the father of the baby is found to be heterozygous or if a patient’s partner is not available for testing, a free fetal DNA test can be done on the mother’s blood to detect the baby’s Rh type. Free fetal DNA is found in the pregnant woman’s bloodstream as early as 10 weeks of gestation due to leakage of DNA material from the placenta. Currently the free fetal DNA test is only available for determining the Rh type of the fetus; testing for other red cell antigens is not yet available.
A special type of ultrasound called Doppler can be used to measure the speed of your baby’s blood as it moves through a particular blood vessel in the baby’s brain. This vessel is called the middle cerebral artery (MCA). As babies become anemic, they increase the speed of the blood that moves through their body in order to deliver more oxygen to their tissues. The top speed of the blood moving through the MCA is then compared to a normal value for the point in pregnancy when it is being measured. The test result is reported as the multiples of the median or MOM’s. A test result more than one and a half times higher than the usual value (> 1.5 MOM’s) indicates that the baby is likely to be anemic. MCA measurements can be started as early as 16 weeks of pregnancy and are usually repeated every 1 – 2 weeks.
This test is usually not performed unless the MCA Doppler is abnormal. It involves drawing some blood from your baby while the baby is still inside your womb. This procedure is known as Cordocentesis or Umbilical Blood Sampling. The procedure is very much like amniocentesis with the exception that instead of inserting the needle into the bag of waters around the baby, your doctor will direct a needle with ultrasound into the umbilical cord to get a sample of blood. This method enables your doctor to perform a variety of tests to predict the severity of disease in your baby. These include confirmation of blood type, blood count (hematocrit), number of new blood cells being made by the baby (reticulocyte count), and the amount of antibody attached to the baby’s red blood cells (direct Coombs).
What is hemolytic disease of the fetus and newborn? »
Treatment for hemolytic disease of the fetus and newborn »
Hemolytic disease of the fetus and newborn frequently asked questions »
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The Fetal Center at Children's Memorial Hermann Hospital
UT Professional Building
6410 Fannin, Suite 210
Houston, TX 77030
Toll free:(888) 818-4818