The Rh Factor and Rhogam

Along with the different blood groups such as A, B, and O, there is the Rh factor. The Rh factor is a type of protein found on the surface of blood cells in about 85% of the general population. 15% of the population does not have this protein on the surface of their blood cells and they are considered Rh negative. At your first prenatal visit, your blood type and Rh status will be determined because there are special implications for pregnancy.

Although the fetal blood circulation and the maternal blood circulation are separate, it is possible for fetal blood to intermix with maternal blood under certain circumstances. If a woman is Rh negative and her baby is Rh positive and there is some intermixing during pregnancy or childbirth, the woman’s immune system will recognize the baby’s blood cells as foreign. She will develop antibodies to the foreign cells in a process called sensitization. Usually in a first pregnancy, the immune response by the mother to foreign blood cells is very weak, and does not cause a problem. In future pregnancies, however, once the immune system is ‘primed’, the reaction can be quite severe and life threatening for the unborn baby. The antibodies to the foreign blood cells can cross the placenta and attack and destroy the fetal blood. This produces anemia in the baby, which when severe, can lead to serious problems or even death. The medical terms for this process are isoimmunization leading to hemolytic disease of the newborn. A lay term used commonly in the past was blue baby syndrome.

Rhogam or anti-Rh immunoglobulin was developed in the 1960s by Dr. Vincent Freda, a professor of obstetrics and gynecology at Columbia University. Rhogam has practically erradicated immune hemolytic disease of the newborn by preventing isoimmunization. It is an intramuscular injection given during pregnancy to all Rh negative mothers at 28 weeks and/or at the time of events that we know are associated with intermixing of fetal and maternal blood such as amniocentisis, CVS, pregancy termination, or miscarriage. Rhogam works by coating foreign fetal cells in the maternal circulation and ‘hiding’ them from the mothers immune system until they are out of her system.  After delivery, if the baby of an Rh negative mom is proven to be Rh positive, she is again given Rhogam within 72 hours of delivery.


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