Rho(D) immune globulin (RhIG) is a medication used to prevent RhD isoimmunization in mothers who are RhD negative and to treat idiopathic thrombocytopenic purpura (ITP) in people who are Rh positive. It is often given both during and following pregnancy. It may also be used when RhD-negative people are given RhD-positive blood. It is given by injection into muscle or a vein. A single dose lasts 12 weeks.Common side effects include fever, headache, pain at the site of injection, and red blood cell breakdown. Other side effects include allergic reactions, kidney problems, and a very small risk of viral infections. In those with ITP, the amount of red blood cell breakdown may be significant. Use is safe with breastfeeding. Rho(D) immune globulin is made up of antibodies to the antigen Rho(D) present on some red blood cells. It is believed to work by blocking a persons immune system from recognizing this antigen.Rho(D) immune globulin came into medical use in the 1960s. It is on the World Health Organizations List of Essential Medicines. It is made from human blood plasma. Medical uses
In a pregnancy where the mother is RhD negative and the father is RhD positive, the probability of the fetus having RhD positive blood is dependent on whether the father is homozygous for RhD (i.e., both RhD alleles are present) or heterozygous (i.e., only one RhD allele is present). If the father is homozygous, the fetus will necessarily be RhD positive, as the father will necessarily pass on a Rh D positive allele.
If the father is heterozygous, there is a 50% chance that the fetus will be RhD positive, as he will randomly pass on either the RhD positive allele or not.If a fetus is RhD positive and the mother is RhD negative, the mother is at risk of RhD alloimmunization, where the mother mounts an immune response (develops antibodies) to fetal red blood cells. This usually has minimal effect on the first such pregnancy; but, in a second such pregnancy, pre-existing maternal antibodies to RhD antigens on fetal red blood cells often leads to erythroblastosis fetalis, a condition which can be fatal to the fetus. In countries without Rh immune globulin (RhIG) protocols, as many as 14% of affected fetuses are stillborn and 50% of live births result in neonatal death or brain injury.Because of this severe complication, the American College of Obstetricians and Gynecologists (ACOG) recommends that all RhD negative mothers, regardless of fetal blood type, receive RhIG at about 28 weeks gestation, and again shortly after delivery in the case of an RhD positive or RhD unknown baby. It should be given within 3 days of a potential exposure to Rh positive blood from the baby such as may occur during second or third trimester miscarriage, amniocentesis, cordocentesis, chorionic villus sampling, external cephalic version, trauma, or delivery. It should be considered after first trimester miscarriage. The 28 weeks recommendation comes from the fact that 92% of women who develop an anti-D during pregnancy do so at or after 28 weeks gestation.