About eighty-five percent of the people in this country have a substance contained in the red cells of their blood. This is known as the Rhesus factor, or more commonly, the Rh factor.

When a person’s blood contains the Rh factor, they are referred to as being Rh positive (Rh+), and those persons whose blood do not contain the Rh factor, are Rh negative (Rh-).

If a Rh- person receives Rh+ blood, the destruction of the red corpuscles of their blood usually occurs. This hemolytic disease also could happen if a woman’s blood is Rh- and she is carrying a baby whose blood is Rh+.

The transfer of the blood between the fetus and the mother would cause the woman’s blood system to produce Rh antibodies because her immune system would act as though the fetal blood cells were "foreign."

Very few first-pregnancy babies are damaged as the Rh antibodies have not formed sufficiently to harm the first baby. However, a previous miscarriage, abortion, or amniocentesis in which the fetus’s blood was Rh+ might have sensitized the woman. During subsequent pregnancies, antibodies can cross the placenta and attack the fetal blood cells. This causes the destruction of fetal red corpuscles and results in anemia of the newborn. Death or permanent damage to the infant often results.

Rhesus hemolytic disease of a newborn infant was first described in medical literature almost 400 years ago – in year 1609. It has only been about 70 years since the cause of the disorder was technically described, and only 30 years since antibody prevention treatments have been available.

Medication to prevent Rhesus disease was approved for use in the US during 1968. Rhesus immune globulin (also known as RhoGAM) is administered to the Rh- woman with a Rh+ partner any time there is chance fetal cells may enter the pregnant woman’s circulation. It is routinely administered at 28 weeks of pregnancy and after the delivery of an Rh+ infant. This prevention treatment has resulted in about an 80% reduction in the number of babies with RhHDN, but the disease still occurs all too freq-uently.

The Rh hemolytic disease of the newborn (RhHDN) use to occur quite frequently – about one case of RhHDN disease per 200 live births. During the year 1970 before treatment was readily available, there were over 1,550 cases reported in the state of California. During that timeframe, this disease accounted for about 10% of the early deaths of infants.