The antibody anti-Rho(D) is responsible for most severe instances of hemolytic disease of the newborn (erythroblastosis fetalis). About 15% of whites and much lower proportions of blacks and Asians are Rho(D)-negative. If an Rho(D)-negative woman carries an Rho(D)-positive fetus, she may develop antibodies against Rho(D) when fetal red cells enter her circulation during small fetomaternal bleeding episodes in the early third trimester or during delivery, abortion, ectopic pregnancy, abruptio placentae, or other antepartum bleeding problems. This antibody, once produced, remains in the woman’s circulation and poses the threat of hemolytic disease for subsequent Rh-positive fetuses.

Passive immunization against hemolytic disease of the newborn is achieved with Rho(D) immune globulin, a purified concentrate of antibodies against Rho(D) antigen. The Rho(D) immune globulin (one vial of 300 ug intramuscularly) is given to the mother within 72 hours after delivery (or spontaneous or induced abortion or ectopic pregnancy). The antibodies in the immune globulin destroy fetal Rh-positive cells so that the mother will not produce anti-Rho(D). During her next Rh-positive gestation, erythroblastosis will be prevented. An additional safety measure is the administration of the immune globulin at the 28th week of pregnancy. The passive antibody titer that results is too low to significantly affect an Rh-positive fetus. The maternal clearance of the globulin is slow enough that protection will continue for 12 weeks.

Hemolytic disease of varying degrees, from mild to serious, continues to occur in association with Rh subgroups (C, c, or E) or Kell, Kidd, and other factors. Therefore, the presence of atypical antibodies should be checked in the third trimester of all pregnancies.

Moise KJ Jr: Management of rhesus alloimmunization in pregnancy. Obstet Gynecol 2002;100:600.

Prevention of Rh D alloimmunization. Clinical management guidelines for obstetrician-gynecologists. ACOG Practice Bulletin No. 4, 1999. Int J Gynaecol Obstet 1999;66:63.