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What are the implications if parents have different Rh factors?

Q: I am 29 years old and got married 3 months back. My blood group is O (+ve) and my wife's is O (-ve). What complications can arise for my wife's pregnancy? What precautions do we need to take while planning a pregnancy?

A:A. When we talk about ‘+’ or ‘-’ with respect to blood group, we are referring to the Rh factor (i.e., rhesus factor). This is a red blood cell surface antigen that was named after the monkeys in which it was first discovered. Rh incompatibility is a complication, also known as Rh disease, that occurs when a woman with Rh-negative blood type is exposed to Rh-positive blood cells, leading to the development of Rh antibodies. Rh incompatibility can occur by two main mechanisms. The most common type occurs when an Rh-negative pregnant mother is exposed to Rh-positive fetal red blood cells secondary to fetomaternal haemorrhage during the course of pregnancy from spontaneous or induced abortion, trauma, invasive obstetric procedures, or delivery. Rh incompatibility can also occur when an Rh-negative female receives a blood transfusion that contains Rh antigens The most common cause of Rh incompatibility is exposure to an Rh-negative mother by Rh-positive fetal blood during pregnancy or delivery, whereby red blood cells from the fetal circulation leak into the maternal circulation. After a significant exposure, sensitisation occurs and maternal antibodies are produced against the foreign Rh antigen. Once produced, maternal Rh immunoglobulin G (IgG) antibodies may cross freely from the placenta to the fetal circulation, where they form antigen-antibody complexes with Rh-positive fetal erythrocytes and eventually are destroyed, resulting in a fetal alloimmune-induced haemolytic anaemia. Although the Rh blood group systems consist of several antigens (e.g., D, C, c, E, e), the D antigen is the most immunogenic; therefore, it most commonly is involved in Rh incompatibility. Most firstborn infants with Rh-positive blood type are not affected because the short period from first exposure of Rh-positive fetal erythrocytes to the birth of the infant is insufficient to produce a significant maternal IgG antibody response. The risk and severity of sensitisation response increases with each subsequent pregnancy involving a fetus with Rh-positive blood. In women who are prone to Rh incompatibility, the second pregnancy with an Rh-positive fetus often produces a mildly anaemic infant, whereas succeeding pregnancies produce more seriously affected infants who ultimately may die in utero from massive antibody-induced haemolytic anaemia. Prevention: If the mother has Rh-negative blood and has not been sensitised previously, administer human anti-D immune globulin (Rh IgG) and refer the woman to an obstetrician for further evaluation. The drug: Human anti-D immune globulin (RhoGAM) -- Suppresses immune response of non-sensitised Rh O (D) negative mothers exposed to Rh O (D) positive blood from the fetus as a result of a fetomaternal haemorrhage, abdominal trauma, amniocentesis, abortion, full-term delivery, or transfusion accident. Should be administered if the patient is Rh-negative, unless the father also is Rh-negative Adult Dose <13 wk gestation: 50 mcg IM; >13 wk gestation: 300 mcg IM Contraindication: Documented hypersensitivity; patients who have received Rho(D)-positive blood within the last 3 months. Precautions: Caution in thrombocytopaenia, bleeding disorders, or IgA deficiency; when administered close to delivery, may interfere with Rh typing of the newborn.


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