An Rh-negative mother who was exposed to her fetus's Rh-positive blood during a previous pregnancy or delivery or who has accidentally received an Rh-positive blood transfusion has antibodies against Rh-positive blood cells.
Therefore, all mothers who have Rh-negative blood and no apparent sensitization (as indicated by antibody titer) should be treated with a standard 300g dose of Rh(D) immune globulin (Rhogam) at about 28 weeks of gestation.
If the Rh-negative woman is not isoimmunized, a repeat antibody determination is done around 28 weeks' gestation, and the expectant woman should receive an injection of an anti-Rh (D) gamma globulin called Rhogham.
Only 15 to 16 percent of the Caucasian population is Rh-negative, compared to approximately 8 percent of the African-American population and significantly lower in Asian populations.
Rh incompatibility may develop when a woman with Rh-negative blood becomes pregnant by a man with Rh-positive blood and conceives a fetus with Rh-positive blood.
Rh disease, for example, has been controlled by the advent of anti-Rh globulin; its administration to Rh-negative mothers has reduced one risk factor for CP.
If the father is Rh-positive, an antibody screen is done to determine whether the Rh-negative woman is sensitized to the Rh antigen (developed isoimmunity).
A person with at least one copy of the gene for the Rh factor has Rh-positive blood; if no copies are inherited, the person's blood type is Rh-negative.
Conversely, a woman sensitized by previous Rh-positive fetuses may have a high antibody titer during her pregnancy while the fetus is Rh-negative.
If an Rh-negative woman gives birth to an Rh-positive baby, she is given an injection of Rhogam within 72 hours of the birth.