Rhesus incompatibility in pregnancy

Updated: Sep 5, 2020

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The whole human body is made up of cells, cells performing the same or similar functions come together to form tissues. Blood is a tissue existing in the liquid form and it's formed by the combination of white blood cells (WBCs) or the Leukocyte performing the immune function, Red blood cells (RBCs) or the Erythrocytes performing the function of oxygen and other gases transportation, blood platelets or the thrombocytes. Both WBCs and RBCs come into play in this presentation.

Rhesus factors are antigenic proteins found on the surfaces of the red blood cells and are genetically inherited like other genes.

If a person blood cells has this protein, the person is said to be Rhesus positive. If a person blood cells does not have this protein, the person is said to be Rhesus negative. The Rhesus factor determines if the blood of two different people is compatible when mixed, such as the blood of a mother and her baby.

Being Rhesus positive or negative is not a bad thing, it is like your hair or eye colour in the sense that they are just inherited traits. However, Rhesus incompatibility can be very problematic when it comes to having children. Rhesus incompatibility is a condition which develops when there is a difference in Rhesus blood type between the pregnant mother (Rhesus negative) and that of the fetus (Rhesus positive).

Rhesus incompatibility together with ABO blood incompatibility are the major cause of hemolytic disease of the fetus and the newborn (HBFN) or what is been called erythroblastosis fetalis.

Any process or processes that can bring the fetal blood in contact with the mother blood is poss as risk for rhesus incompatibility. The followings among others are the risk factors.

  • Early delivery

  • complications such as miscarriages, ectopic pregnancies, or termination of pregnancies

  • Injury to the stomach area during pregnancy

  • Bleeding during pregnancy (fetomaternal bleeding)

  • Tests that require cells or fluids to be withdrawn from a pregnant woman (like amniocentesis and chorus villus sampling)

  • Delivery of a baby (either vaginal or cesarean)

The pathophysiologic processes occur in two phases; first pregnancy which is the sensitization phase and the second pregnancy.

This occurs when a rhesus negative mother is a having a fetus that has inherited a rhesus positive gene from the father and it usually occur in the first pregnancy. When the fetal RBCs mix with the mother blood, the mother WBCs produce antibody against against this rhesus antigen located on the surfaces of the fetal RBCs. The first born is not affected by this process but the subsequent pregnancy does. This takes place during child delivery, abortion, bleeding during pregnancies and any other conditions that will cause the fetal blood to mix with the maternal blood.

IgM cannot cross the fetal placenta. When there is a repeat encounter with fetal Rhesus antigen, there is rapid production of IgG antibody by mother's WBCs. This IgG traverses the placenta, attaches the fetal RBCs and the mark them for destruction because it sees them as exobiotics. This effect initiated by the macrophages and the natural killer B-lymphocyes causes the lysis of the antibody-RBCs complexes in the spleen and other tissues resulting into hemolytic anemia.

The hemolysis of the fetal red bloods cells results into many signs and symptoms. The consequences of this hemolysis are anema, jaundice, hydrops fetalis characterize by general body edema as result of hypoalbuminamia caused by the destruction of the hepatic parenchyma. Unconjugated bilirubin crosses the blood brain barrier and damages the basal ganglia, cardiopulmonary system collapsed because of low blood volume or hypovolumic shock. There is usually low muscle tone.

The prevention is done by administering rhesus immunoglobulin at the dose of 1500 I.U (300 microgram) at 28-32 weeks of pregnancy and within 72 hours postpartum or any process (amniocentesis, fetomaternal hemorrhage, etopic pregnancy, abortion e.t.c) that could result into sensitization of the maternal antibody.

In mild cases, the baby can be treated after birth with a series of compacted hemoglobulin blood transfusion, fluid hydration to increase blood volume. Phototherapy at the range of 415-490 nm of UV light. This process is done with the baby face covered. Phototherapy induces photo-oxidation of the bilirubin that subsequently reduces it concentration of bilirubin in the body.

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