RHIg

RhIG, or Rh immune globulin, is an anti-D immunoglobulin preparation used to prevent RhD sensitization in Rh-negative pregnant people carrying an Rh-positive fetus. By preventing maternal formation of anti-D antibodies, RhIG helps reduce the risk of hemolytic disease of the fetus and newborn in current and future pregnancies.

Mechanism and purpose:

RhIG contains antibodies to the RhD antigen. When fetal RhD-positive red blood cells enter the maternal circulation, the anti-D antibodies bind them and promote their clearance, inhibiting the maternal immune response to D antigen and thereby preventing alloimmunization.

Indications and timing:

RhIG is given to Rh-negative pregnant individuals who are not already alloimmunized. Routine antenatal prophylaxis is typically administered during pregnancy (often around 28 weeks gestation) and postpartum within 72 hours after birth if the newborn is Rh-positive. Additional doses are given after events that can cause fetomaternal hemorrhage, such as miscarriage, abortion, chorionic villus sampling, amniocentesis, ectopic pregnancy, or significant abdominal trauma. The dose and route may vary by formulation and clinical scenario; dosing after a potential hemorrhage may be guided by tests estimating fetal-metal hemorrhage.

Formulation and administration:

RhIG is derived from human plasma and administered by intramuscular injection in most settings; some products permit intravenous use. Brands include examples such as RhoGAM and Rhophylac, among others.

Safety and contraindications:

RhIG is generally well tolerated; common effects are mild and local. Rare severe reactions can occur. It is not given to women who are already known to be alloimmunized against the D antigen.

Impact:

When used appropriately, RhIG significantly lowers the incidence of RhD alloimmunization and reduces the risk of HDFN in subsequent pregnancies.