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Blood group testing confirms your blood type. In general, about 46 percent of people have type O blood, 42 percent have type A, 9 percent have type B and 3 percent have type AB. This information, along with antibody screening and Rh testing, can be used to identify the appropriate blood supply in the event of a blood transfusion.
You'll also get an Rh factor test during your first visit, or shortly thereafter. If you're Rh negative and your baby's father is Rh positive, there's a 70 to 75 percent chance that your baby will be Rh positive as well, meaning that you and your baby are not Rh compatible. This case warrants treatment with Rh immunoglobulin (RhoGAM) at 28 weeks' gestation to ensure that you don't develop isoimmunization '- a buildup of antibodies against your own baby's blood '- which isn't likely to cause problems this time around but may put later pregnancies with an Rh-negative baby at risk.
In addition to the third trimester dose of RhoGAM, Rh-negative moms-to-be should also get this treatment if they experience any of the following: a first trimester pregnancy loss (spontaneous, induced or ectopic), an amniocentesis or chorionic villus sampling, antepartum bleeding or significant abdominal trauma during pregnancy. If you're Rh negative, your baby will have an Rh factor test, and you'll get another 300 micrograms of RhoGAM within 72 hours of delivery if your baby tests Rh positive. RhoGAM treatments before and after delivery, and in the event of any other procedures or trauma that can result in the baby's blood leaking into the mother's body, prevent more than 99 percent of possible Rh isoimmunization cases.
Red Cell Antibody Screening
Besides the rhesus antibody (Rh), there are several other antibodies present in a mother that can cause problems for a baby if gone undetected. Such antibodies can attack the red blood cells of the baby, causing them to "hemolyze," or break apart. In severe cases, the baby develops hemolytic disease of the newborn (HDN), which makes the baby anemic and limits the ability of the blood to carry oxygen to baby's organs and tissues. The baby's body naturally responds by trying to make more red blood cells very quickly in the bone marrow, liver and spleen, causing these organs to get bigger. But the new red blood cells are not able to do the work of mature red blood cells. Babies may develop this condition while still in the uterus (erythroblastosis fetalis) and need specialized monitoring, an intrauterine transfusion or early delivery. As the red blood cells break down, a substance called bilirubin is formed. Babies are not easily able to get rid of the bilirubin, and it can build up in the blood and other tissues and fluids of baby's body, causing hyperbilirubinemia. Because bilirubin has a pigment, or coloring, it causes a yellowing of the baby's skin and tissues '- jaundice.
When mothers build up antibodies in sufficient amount (maternal sensitization), the fetus is at risk for erythroblastosis fetalis and the baby at risk for HDN. Some of the antibodies leading to this are known as C, c, E, e, Kell, Duffy and Kidd. If your test reveals the presence of these antibodies, tests called titers will follow during the pregnancy. You'll also be a candidate for ultrasound and nonstress testing, and you'll want to seek the care of a perinatologist.