Rh incompatibility

Rh incompatibility or Rh disease (also known as Rh (D) disease, Rhesus disease, RhD Hemolytic Disease of the Newborn, Rhesus D Hemolytic Disease of the Newborn or RhD HDN) is one of the causes of hemolytic disease of the newborn (also known as HDN). The disease ranges from mild to severe. When the disease is mild the fetus may have mild anaemia with reticulocytosis. When the disease is moderate or severe the fetus can have a more marked anaemia and erythroblastosis (erythroblastosis fetalis). When the disease is very severe it can cause morbus haemolyticus neonatorum, hydrops fetalis, or stillbirth.

Serology
During any pregnancy a small amount of the baby's blood can enter the mother's circulation. If the mother is Rh negative and the baby is Rh positive, the mother produces antibodies (including IgG) against the Rhesus D antigens on her baby's red blood cells. During this and subsequent pregnancies the IgG is able to pass through the placenta into the fetus and if the level of it is sufficient, it will cause a Rhesus D positive fetus to develop Rh disease. The mechanism is maternal anti-D IgG passing through the placenta to the fetus causing destruction of fetal red blood cells. Generally Rhesus disease becomes worse with each additional Rhesus incompatible pregnancy. The main and most frequent sensitizing event is child birth (about 86% of sensitized cases), but fetal blood may pass into the maternal circulation earlier during the pregnancy (about 14% of sensitized cases). Sensitizing events during pregnancy include miscarriage, therapeutic abortion, amniocentesis, ectopic pregnancy, abdominal trauma and external cephalic version.

The incidence of Rh disease in a population depends on the proportion that are rhesus negative. Many non-caucasian peoples have a very low proportion who are Rhesus negative, so the incidence of Rh disease is very low in these populations. In Caucasian populations about 1 in 10 of all pregnancies are of a Rhesus negative woman with a Rhesus positive baby. It is very rare for the first Rhesus positive baby of a Rhesus negative woman to be affected by Rh disease. The first pregnancy with a Rhesus positive baby is significant for a rhesus negative woman because she can be sensitized to the Rh positive antigen. In Caucasian populations about 13% of Rhesus negative mothers are sensitized by their first pregnancy with a rhesus positive baby. If it were not for modern prevention and treatment, about 5% of the second Rhesus positive infants of Rhesus negative woman, would result in still births or extremely sick babies and many babies who managed to survive would be severely ill. Even higher disease rates would occur in the 3rd and subsequent Rhesus positive infants of rhesus negative woman. By using anti-RhD immunoglobulin (Rho(D) Immune Globulin) the incidence is massively reduced.

Rh disease sensitization is about 10 times more likely to occur if the fetus is ABO compatible with the mother than if the mother and fetus are ABO incompatible.

Prevention
Most Rh disease can be prevented by treating the mother during pregnancy or promptly (within 72 hours) after childbirth. The mother has an intramuscular injection of anti-Rh antibodies (Rho(D) Immune Globulin), so that the fetal Rhesus D positive erythrocytes are destroyed before her immune system can discover them. This is passive immunity and the effect of the immunity will wear off after about 4 to 6 weeks (or longer depending on injected dose) as the anti-Rh antibodies gradually decline to zero in the maternal blood.

It is part of modern antenatal care to give all Rhesus D negative pregnant women an anti-RhD IgG immunoglogbulin injection at about 28 weeks gestation (with or without a booster at 34 weeks gestation). This reduces the effect of the vast majority of sensitizing events which mostly occur after 28 weeks gestation. Anti-RhD immunoglobulin is also given to non-sensitized Rhesus negative women immediately (within 72 hours - the sooner the better) after potentially sensitizing events that occur earlier in pregnancy.

Blood tests
Maternal blood


 * The Kleihauer-Betke test or flow cytometry on a postnatal maternal blood sample can confirm that fetal blood has passed into the maternal circulation and can also be used to estimate the amount of fetal blood that has passed into the maternal circulation.


 * The indirect Coombs test is used to screen blood from antenatal women for IgG antibodies that may pass through the placenta and cause hemolytic disease of the newborn.

Fetal blood (or umbilical cord blood)


 * The direct Coombs test is used to confirm that the fetus or neonate has an immune mediated hemolytic anemia.


 * Full blood count - the hemoglobin level and platelet count are important


 * Bilirubin (total and indirect)

Management
Antenatal
 * Ultrasound - to detect and monitor hydrops fetalis
 * Quantitative analysis of maternal anti-RhD antibodies - an increasing level is a sign of fetal Rh disease
 * Intrauterine blood transfusion
 * Intraperitoneal transfusion - blood transfused into fetal abdomen
 * Intravascular transfusion - blood transfused into fetal umbilical vein - This is more modern and more effective than intraperitoneal transfusion. A sample of fetal blood can be taken from the umbilical vein prior to the transfusion.
 * Early delivery (usually after about 36 wks gestation)

Postnatal
 * Phototherapy for neonatal jaundice in mild disease
 * Exchange transfusion if the neonate has moderate or severe disease (the blood for transfusion must be less than a week old, Rh negative, ABO compatible with both the fetus and the mother, and be cross matched against the mothers serum)

History of medical advances in Rh disease
The rhesus blood type was first discovered in 1937 by Karl Landsteiner and Alexander S. Wiener.

In 1939 Philip Levine and Rufus E. Stetson published their findings about a family who had a stillborn baby who died of hemolytic disease of the newborn. The mother was aged 25 and it was her second pregnancy and she suffered blood loss at the delivery. Both parents were blood group O and the husband's blood was used to give the mother a blood transfusion, but the mother suffered a severe transfusion reaction. They investigated this transfusion reaction. Since the mother and the father were both blood group O, they concluded that there must be a previously undiscovered blood group antigen that was present on the husband's RBCs but was not present on the mother's RBCs and that the mother had formed antibodies against the new blood group antigen. This suggested for the first time that a mother could make blood group antibodies because of immune sensitization to her fetus's RBCs. They did not name this blood group antigen, but it was subsequently found to be the Rhesus factor.

The first treatment for Rh disease was an exchange transfusion, which was invented by Dr. Alexander S. Wiener. That procedure was further refined by Dr, Harry Wallerstein, a transfusionist. Although the most effective method of treating the problem at the time, it was only partially ameliorative in cases where damage to the neonate had already been done. Children with severe motor damage and/or retardation could result. However, it is estimated that in the two decades it was used approximately 200,000 lives were saved, and the great majority were not brain damaged.

Ronald Finn, in Liverpool, England applied a microscopic technique for detecting fetal cells in the mother's blood. It led him to propose that the disease might be prevented by injecting the at-risk mother with an antibody against fetal red blood cells. He proposed this for the first time to the public on February 18, 1960. A few months later, he proposed at a meeting of the British Genetical Society that the antibody be anti-RhD.

Nearly simultaneously with him, William Pollack, then of Ortho Pharmaceutical Corporation, and researchers John Gorman and Vincent Freda of New York City's Columbia-Presbyterian Medical Center, having come to the same realization, set out to prove it by injecting a group of male prisoners at Sing Sing Correctional Facility with antibody provided by Ortho, obtained by a fractionation technique developed by Dr Pollack (who also provided Dr. Finn with several vials of antibody during a visit by Dr. Finn to Ortho).

Animal studies had previously been conducted by William Pollack, using a rabbit model of Rh. This model, named the rabbit HgA-F system, was a perfect animal model of human Rh, and enabled Dr. Pollack's team to gain experience in preventing hemolytic disease in rabbits by giving specific HgA antibody, as was later done with Rh-negative mothers. One of the needs was a dosing experiment that could be used to determine the level of circulating Rh-positive cells in an Rh-negative pregnant female derived from her Rh-positive fetus. This was first done in the rabbit system, but subsequent human tests at the University of Manitoba conducted under Dr. Pollack's direction confirmed that this result matched the human dosing perfectly. The dose is 20 µG of antibody for 1mL of Rh-positive red cells.

Dr. Gorman's sister-in-law was the first at risk woman to receive a prophylactic injection on January 31, 1964. Clinical trials set up by Dr. Pollack in 42 clinical centers in the US, Great Britain, Germany, Sweden, Italy, and Australia confirmed their hypothesis, and the vaccine was finally approved in England and the United States in 1968. The FDA approved the drug under the name RhoGAM, with a fixed dose of 300 µG, to be given within three days postpartum. There being no known harm done by delaying the dosage for a week or more after birth, Ortho asked the FDA to grant permission for it to be given without a postpartum time restriction. In addition, Dr. John M. Bowman, one of the researchers at the University of Manitoba, and Dr Freda pushed to allow antepartum use. All of this was subsequently granted. Within a year or so, the antibody had been injected with great success into more than 500,000 women. Time magazine picked it as one of the top ten medical achievements of the 1960's. By 1973, it was estimated that in the US alone, over 50,000 babies' lives had been saved. The use of Rh immune globulin to prevent the disease in babies of Rh negative mothers has become standard practice, and the disease, which used to claim the lives of 10,000 babies each year in the US alone, has been virtually eradicated in the developed world. In 1980 Drs. Pollack, Gorman, Freda, and Finn shared the Albert Lasker Award for their work on Rh disease.

Two of the Canadian researchers from the University of Manitoba, Dr. Bruce Chown and Dr. John M. Bowman, licensed a version of the vaccine, known as WinRho SD, in 1980. The drug is sold in 35 countries by the Manitoba-based research firm Cangene, listed on the Toronto Stock Exchange with worth of about $175 million. Cangene was purchased by the Winnipeg Rh Institute, a facility founded by Chown and Bowman and dedicated to conducting research into blood related diseases. Dr. Chown is honored by the Canadian Medical Hall of Fame for his lifelong work with erythroblastosis fetalis.