Why Prenatal Testing For Rhesus D Is Important...
A blood test can determine your blood type and Rhesus D (RhD) factor. This information will help your physician determine if there is an increased risk of RhD incompatibility of blood types between you and your baby and, if necessary, make informed treatment decisions.
A new noninvasive laboratory test that can determine the RhD status of your baby is now available from the Sequenom Center for Molecular Medicine. This new test, ordered by your physician, requires only a blood sample from the mother.
What Is Rhesus D?
People have one of four blood types, A, B, AB or O. Each of these are further classified according to the presence or absence of Rh factor proteins on the surface of red blood cells, which carry the Rhesus antigens. One of the main antigens is D. If the protein is present,it is called RhD positive; if it is not present, it is called RhD negative. About 85% of Caucasians are RhD positive, while 92-98% of African American and Hispanic populations and 98-99% of Asian and Native American populations are RhD positive. Between half and all the children born to an RhD negative mother and RhD positive father will be RhD positive.
What Is RhD Incompatibility?
RhD incompatibility in pregnancy occurs when the mother is negative for the Rhesus D factor and the baby is positive. There is a risk that during pregnancy, the baby’s blood cells might enter the mother’s bloodstream causing the mother to produce antibodies that destroy and eliminate the baby’s red blood. This immune response may lead to RhD disease.
Normally this does not occur during a first pregnancy. However, during birth a mother and her baby’s cells can mix together and a mother may develop antibodies that could cause RhD disease in her future pregnancies.
What Is RhD Disease?
RhD Disease can result in jaundice, anemia, brain damage, heart failure or even fetal death. Without treatment, severe cases may result in stillborn deliveries.
What Treatment Is Available?
If you are RhD negative, your doctor may give you two Rh immune-globulin (Rh Ig) injections, one at 28 weeks and a second within 72 hours after birth, which will help to prevent you from developing the damaging RhD antibodies if you are carrying a baby who is RhD positive.
If your doctor determines that you have already developed RhD antibodies and are at risk, s/he will closely monitor your baby’s health and may recommend further tests such as blood tests, amniocentesis, Doppler ultrasound or cordocentesis.
What is RHD Genotyping?
A noninvasive RHD genotyping test is now available that can determine the RhD status of your baby by a blood test. Your physician can recommend this genetic test to tell early in your pregnancy whether your baby is Rhesus D positive or negative, and determine the proper care for you and your baby.
For more information, ask your doctor about fetal RHD genotype testing.