Rhesus disease is a condition which affects an unborn baby when its mother’s immune system generates antibodies which attack the baby’s red blood cells. Pregnant women do not display any symptoms, but babies born with this disease often have anemia and jaundice. Rhesus disease was once very common in women with certain blood types, but is now relatively rare, as it can be prevented with a simple injection. This condition is also called Rh (D) disease, or hemolytic disease of the newborn.
The term Rh (D) refers to a protein called Rhesus factor D. This protein is present on the surface of red blood cells in people who are said to be Rhesus-positive. Not all people are Rhesus-positive; those who do not have the Rhesus factor D protein are said to be Rhesus-negative.
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For Rh (D) disease to develop in an unborn baby, two conditions must be met. First, there is a risk of Rhesus disease developing when a woman with the Rhesus-negative blood type is pregnant with a baby who has Rhesus-positive blood. For the disease to actually develop, however, the pregnant woman must have previously been exposed to Rhesus-positive blood. This second condition must be met in order for the woman’s immune system to generate antibodies to the Rhesus-positive blood cells of the baby.
A typical scenario in which Rhesus disease develops is when a pregnant woman with the Rhesus-negative blood type has previously given birth to a baby with the Rhesus-positive blood type. In this situation, her immune system was exposed to Rhesus factor D during the first pregnancy. This initial exposure is called sensitization. In her second pregnancy, if this baby is also Rhesus-positive, the woman’s immune system will generate antibodies which attack the baby’s red blood cells. These antibodies can cross the placental barrier from mother to child and destroy fetal red blood cells.
Up until the late 1970s, Rhesus disease was a relatively common neonatal complication. In 1977, a preventative injection was introduced which stops the immune system from developing antibodies to Rhesus factor D. The injection contains antibodies which recognize Rhesus factor D, and destroy red blood cells which are Rhesus-positive. This is called anti-D immunoglobulin, and is given to all Rhesus-negative women who are pregnant.
This treatment works because it is given to a woman before her own immune system develops Rhesus factor D antibodies, at around 28 weeks of pregnancy. A Rhesus-negative woman receives this injection each time she is pregnant, ensuring that her immune system never becomes sensitized to produce destructive antibodies.