ERYTHROBLASTOSIS FETALIS: Cause, Treatment and Prevention.

What is erythroblastosis fetalis?

Erythroblastosis Fetalis also known as erythroblastosis neonatorum or Hemolytic Disease of Fetus and Newborn is a disorder in fetus and newborn characterized by the presence of erythroblasts in the blood as a result of hemolytic disease in fetus and newborn which is characterized by abnormal hemolysis of RBCs due to Rh incompatibility. So basically hemolytic disease leads to Erythroblastosis Fetalis.

Before we go further into the causes, treatment and prevention of erythroblastosis fetalis lets discuss Rh factor as an in depth knowledge of Rh factor will aid our discussion of topic in view.

Rh factor

Rh factor is an antigen present in RBC. This antigen was discovered by Landsteiner and Weiner. It was first discovered in Rhesus monkey and hence the name 'Rh factor'.

There are six common types of Rh antigens, each of which is called an Rh factor. These types are designated C, D, E, c, d and e. However, the type D antigen is widely prevalent and considerably more antigenic in humans than other Rh antigens. Persons having this type of antigen are said to be Rh positive (Rh+) without this type D antigen are said to be Rh negative (Rh-).

About 85% of all white people are Rh positive and 15% , Rh negative. In American blacks, the percentage of Rh positive people is about 95, whereas in African blacks, it is virtually 100%.

Rh group system is different from ABO group system because, the antigen D does not have corresponding natural antibody (anti-D). However, if Rh positive blood is transfused to a Rh negative person, anti-D is developed in that person. On the other hand, there is no risk of complications if the Rh positive person receives Rh negative blood.

Inheritance of Rh Antigen

Rhesus factor is an inherited dominant factor. It may be homozygous Rhesus positive with DD or heterozygous Rhesus positive with Dd. Rhesus negative occurs only with complete absence of D (i.e. with homozygous dd).

Consider the diagram below:

When a Rh negative person receives Rh positive blood for the first time, he is not affected much, since the reactions do not occur immediately. But, the Rh antibodies develop within one month. The transfused RBCs which are still present in the recipient's blood are agglutinated. These agglutinated cells are lysed by macrophages. So, a delayed transfusion reaction occurs. But it is usually mild and does not affect the recipient. However, antibodies developed in the recipient remain in the body, so when this person receives Rh positive blood for the second time, the donor RBCs are agglutinated and severe transfusion reactions occur immediately such as transfusion reaction caused by mismatched type A or B blood.

CAUSE OF ERYTHROBLASTOSIS FETALIS

In most instances of erythroblastosis fetalis, the mother is Rh negative and the father Rh positive. When a mother is Rh- and fetus is Rh+ (the Rh factor being inherited form the father), usually the first child escapes the complications of Rh incompatibility. This is because the Rh antigen cannot pass from the fetal blood into the mother's blood through the placental barrier. However, at the time of parturition (delivery of the child), the Rh antigen from fetal blood may leak into mother's blood because of placental detachment. During postpartum period, i.e. within a month after delivery, the mother develops Rh antibody in her blood. When the mother conceives for the second time and if the fetus happens to be Rh+ again, the Rh antibody from the mother's blood crosses the placental barrier(membrane) through diffusion and enters the fetal blood. Thus , the Rh antigen cannot cross the placental barrier, whereas Rh antibody can.

The Rh antibodies now in the fetus cause agglutination of the fetus' red blood cells. The agglutinated red blood cells subsequently hemolyze, releasing hemoglobin into the blood. The fetus' macrophages then convert the hemoglobin into bilirubin, which causes the baby's skin to become yellow (jaundiced). The antibodies can also attack and damage other cells of the body. The jaundiced, erythroblastotic newborn baby is usually anemic at birth, and the anti-Rh agglutinins from the mother usually circulate in the infant's blood for another 1 to 2 months after birth, destroying more and more red blood cells.
The hematopoietic tissues of the infant attempt to replace the hemolyzed red blood cells. The liver and spleen become greatly enlarged and produce red blood cells in the same manner that they normally do during the middle of gestation. Because of the rapid production of red blood cells, many forms of red blood cells, including many nucleated blastic forms are passed from the baby's bone marrow into the circulatory system, hence the name erythroblastosis fetalis.
Although the severe anemia of erythroblastosis fetalis is usually the cause of death, many children who barely survive the anemia exhibit permanent mental impairment or damage to motor areas of the brain because of precipitation of bilirubin in the neuronal cells, causing destruction of many, a condition called Kernicterus.

TREATMENT OF ERYTHROBLASTOTIC NEONATE
One treatment for erythroblastosis fetalis is to replace the neonate's blood with Rh-negative blood. About 400 milliliters of Rh- blood is infused over a period of one and half hours or more while the neonate's own Rh+ blood is being removed. This procedure may be repeated several times during the first few weeks of life, mainly to keep the bilirubin level low and thereby prevent kernicterus. By the time these transfused Rh negative cells are replaced with the infant's own Rh positive cells, a process that requires 6 or more weeks, the anti-Rh agglutinins that had come from the mother will have been destroyed.

PREVENTION OF ERYTHROBLASTOSIS FETALIS

The Rh blood group system is the primary culprit in causing immunization of an Rh-negative mother to an Rh positive fetus. So the first simple way of prevention is to ascertain the compatibility of your  Rhesus factor with that of your partner before getting married or getting involved in any sexual relationship
Also another method of prevention is the use of Rh immunoglobulin globin, an  anti-D antibody that is administered to the expectant mother starting at 28 to 30 weeks of gestation. The anti-D  antibody is also administered to Rh negative women who deliver  Rh positive babies to prevent sensitization of the mothers to the D antigen. This greatly reduces the risk of developing large amounts of D antibodies during the second pregnancy. The anti-D antibody administered also attaches to D antigen sites on the Rh positive fetal red blood cells that may cross the ' and enter the circulation of the expectant mother, thereby interfering with immune response to the D antigen.