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Rh Factor

Rh factor

Rh factor is a protein called an antigen that is found on the red blood cells of most people. (An antigen is any substance that the body considers "foreign" and thus stimulates the body to produce antibodies against it.) Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85 percent of white Americans and 95 percent of African Americans have the Rh factor and are known as Rh-positive. Those without the Rh factor are Rh-negative.

Rh factor in pregnancy

Rh factor plays a critical role in some pregnancies. If a woman who is Rh-negative becomes pregnant by a man who is Rh-positive, the fetus may inherit the Rh factor from its father and be Rh-positive. If the blood of the fetus becomes mixed with the mother's Rh-negative blood, a disease called erythroblastosis fetalis can occur in future pregnancies, resulting in destruction of the fetus's red blood cells, brain damage, and even death.

The mixing of blood does not normally occur but may take place before or during birth if a tear in the placenta (the organ through which nutrients pass from the mother to the fetus) allows some fetal blood to enter the mother's circulatory system. If this happens, the fetus's red blood cells bearing the Rh factor stimulate the mother's white blood cells to produce antibodies against the foreign antigen. The mother's blood is now sensitized to the Rh factor.

Once a mother's blood is sensitized, the antibodies her body produces in response to the Rh antigen can cross the placenta and attach to the red blood cells of any Rh-positive fetus that she carries. This results in the rupture of the fetus's red blood cells, causing anemia (a condition marked by weakness and fatigue due to a reduced number of red blood cells). Severe anemia can lead to heart failure and death. The breakdown of red blood cells also causes the overproduction of a reddish-yellow substance called bilirubin. An infant with high levels of bilirubin will develop jaundice (have a yellowish appearance) and may suffer brain damage.

Prevention of erythroblastosis fetalis

Erythroblastosis fetalis can be prevented by administering a preparation of anti-Rh factor antibodies to an Rh-negative mother whose blood has not yet produced antibodies to the Rh antigen. The preparation, known as Rh immune globulin, rids the mother's blood of fetal red blood cells before she can become sensitized to them. Rh immune globulin is given whenever there is a possibility of fetal blood mixing with maternal blood, such as following childbirth, an abortion, a miscarriage, or prenatal testing.

Treatment for erythroblastosis fetalis

Treatment for erythroblastosis fetalis depends to what extent the fetus is affected by the action of its mother's anti-Rh-factor antibodies. A fetus whose red blood cells are being severely destroyed can be treated

with transfusions (replacement) of Rh-negative blood while it is still in the uterus. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early. The baby's blood is then replaced with Rh-negative blood following birth.

A pregnant woman who is already sensitized to the Rh antigen can have her doctor carefully monitor the level of antibodies in her blood throughout her pregnancy. If the levels rise, the fetus will need special attention. Unfortunately, once a woman is sensitized, she will always produce antibodies when exposed to the Rh antigen.

Words to Know

Antibody: A protein produced by certain cells of the body as an immune (disease-fighting) response to a specific foreign antigen.

Antigen: Any substance that the body considers foreign and that stimulates the body to produce antibodies against it.

Bilirubin: Reddish-yellow substance produced by the breakdown of red blood cells.

Erythroblastosis fetalis: A disease of fetuses and newborns caused by the mixing of fetal Rh-positive blood with maternal Rh-negative blood and resulting in rupture of fetal red blood cells.

Placenta: The organ formed during pregnancy in mammals through which substances are exchanged between mother and fetus.

Protein: Large molecules that are essential to the structure and functioning of all living cells.

Sensitization: The initial exposure to a specific antigen that causes an immune reaction in the body.

[See also Antibody and antigen; Blood ]

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Rh Factor

Rh factor

Rh factor is also called "Rhesus factor" because it was first discovered in the blood of Rhesus monkeys (small monkeys from India often used for experimentation). Rh factor is an antigen, a substance which stimulates the production of antibodies to fight foreign invaders, such as viruses, bacteria and transplanted organs. A given individual either has the antigen already in their blood (they are Rh positive), or they don't (they are Rh negative). A patient's Rh status effects how he or she handles blood transfusions or organ transplants.

History

Prior to the twentieth century, blood and its function was poorly understood. In trying to solve the problem of serious blood loss from injuries, doctors tried to inject (transfuse) blood from another person or animal into the injured patient. In some cases, this worked and the patient recovered. In many more cases, however, the blood transfusion actually harmed the patient, often causing death. No one could predict which type of reaction would occur as a result of a blood transfusion. So, by the beginning of the nineteenth century, most European nations had outlawed the practice of blood transfusion.

About 1900 Austrian-American physician Karl Landsteiner (1868-1943) developed an explanation for the phenomenon of blood rejection. Landsteiner found that human blood serum (the liquid portion of blood surrounding the cells) could be divided into four categories, depending on its ability to cause clotting of red blood cells. He gave these groups the names A, B, AB, and 0 based on what type of clotting antigen they had, if any.

In 1940 Landsteiner discovered another of blood factor antigen, known as Rh. This discovery resulted from Landsteiner's studies with Rhesus monkeys. Landsteiner and his colleagues found that when blood from monkeys was injected into rabbits and guinea pigs, it clotted. This was because of the presence of another antigen that the researchers had not classified before. Landsteiner called this antigen the Rh (Rhesus) factor. Researchers also showed that the factor occurs among some, but not all, humans. It is also inherited.

Importance of Rh Factor

The Rh discovery had immediate practical importance because it explained a relatively common medical disorder known as erythroblastosis fetalis. In this condition, an Rh-negative woman who becomes pregnant with an Rh-positive fetus (an unborn child) sometimes develops anti-bodies against the Rh factor in the fetus. This development usually causes no problem during the woman's first pregnancy, since the number of anti-bodies produced tends to be small.

By the time a second pregnancy occurs, the situation has changed. The number of Rh antibodies produced by the mother's body has become large enough to cause destruction of red blood cells in the fetus. This can result in complications such as anemia (a chronic blood condition characterized by lack of energy), jaundice (a condition in which bile pigments build up in the blood and cause skin, eyeballs and urine to take on a sickly yellow tone) or premature birth. Today, this reaction can be controlled by immunizing Rh negative women after their first pregnancy with a drug known as RhoGam.

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Rh factor

Rh factor, protein substance present in the red blood cells of most people, capable of inducing intense antigenic reactions. The Rh, or rhesus, factor was discovered in 1940 by K. Landsteiner and A. S. Wiener, when they observed that an injection of blood from a rhesus monkey into rabbits caused an antigenic reaction in the serum component of rabbit blood (see immunity). When blood from humans was tested with the rabbit serum, the red blood cells of 85% of the humans tested agglutinated (clumped together). The red blood cells of the 85% (later found to be 85% of the white population and a larger percentage of blacks and Asians) contained the same factor present in rhesus monkey blood; such blood was typed Rh positive. The blood of the remaining 15% lacked the factor and was typed Rh negative. Under ordinary circumstances, the presence or lack of the Rh factor has no bearing on life or health. It is only when the two blood types are mingled in an Rh-negative individual that the difficulty arises, since the Rh factor acts as an antigen in Rh-negative persons, causing the production of antibodies. Besides the Rh factor, human red blood cells contain a large number of additional antigenic substances that have been classified into many blood group systems (see blood groups); however, the Rh system is the only one, aside from the ABO system, that is of major importance in blood transfusions. If Rh-positive blood is transfused into an Rh-negative person, the latter will gradually develop antibodies called anti-Rh agglutinins, that attach to the Rh-positive red blood cells, causing them to agglutinate. Destruction of the cells (hemolysis) eventually results. If the Rh-negative recipient is given additional transfusions of Rh-positive blood, the concentration of anti-Rh agglutinins may become high enough to cause a serious or fatal reaction. The same type of immune reaction occurs in the blood of an Rh-negative mother who is carrying an Rh-positive fetus. (The probability of this situation occurring is high if the father is Rh positive.) Some of the infant's blood may enter the maternal circulation, causing the formation of agglutinins against the fetal red blood cells. The first baby is usually not harmed. But, if the mother's agglutinins pass into the circulation of subsequent fetuses, they may destroy the fetal red blood cells, causing the severe hemolytic disease of newborns known as erythroblastosis fetalis.

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rhesus factor

rhesus factor (Rh factor) An antigen whose presence or absence on the surface of red blood cells forms the basis of the rhesus blood group system. (The factor was first recognized in rhesus monkeys.) Most people possess the Rh factor, i.e. they are rhesus positive (Rh+). People who lack the factor are Rh–. If Rh+ blood is given to an Rh– patient, the latter develops anti-Rh antibodies. Subsequent transfusion of Rh+ blood results in agglutination, with serious consequences. Similarly, an Rh– pregnant woman carrying an Rh+ fetus may develop anti-Rh antibodies in her blood; these will react with the blood of a subsequent Rh+ fetus, causing anaemia in the newborn baby.

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rhesus factor

rhesus factor (Rh factor) (ree-sŭs) n. a group of antigens that may or may not be present on the surface of the red blood cells; it forms the basis of the rhesus blood group system. Most people have the rhesus factor, i.e. they are Rh-positive. People who lack the factor are termed Rh-negative. Incompatibility between Rh-positive and Rh-negative blood is an important cause of blood transfusion reactions and of haemolytic disease of the newborn. See also blood group.
www.blood.co.uk/pages/e13basic.html Explanation of the Rh factor from the National Blood Service

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rhesus factor

rhesus factor (Rh factor) An antigen that occurs on the surface of the red blood cells of some individuals (who are designated rhesus positive, Rh positive, or Rh+) but not of others (who are rhesus negative, Rh negative, or Rh–). An Rh– person will develop anti-Rh antibodies when given Rh+ blood; a subsequent transfusion of Rh+ blood will then cause agglutination. The phenomenon was first detected in rhesus monkeys (see CERCOPITHECIDAE).

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rhesus factor

rhesus factor (Rh factor) Any of a group of antigens found on the surface of erythrocytes (red blood cells). Rh-negative (Rh−) blood lacks the rhesus factor. Rh factor is present in c.85% of humans (Rh+). Rh incompatibility (an Rh− pregnant woman with an Rh+ fetus) can give rise to anaemia in newborn babies. The antigens were first identified in the blood of rhesus monkeys.

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Rhesus factor

Rhe·sus fac·tor / ˈrēsəs/ (abbr.: Rh fac·tor) • n. [in sing.] an antigen occurring on the red blood cells of many humans (around 85 percent) and some other primates. It is particularly important as a cause of hemolytic disease of the newborn and of incompatibility in blood transfusions.

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rhesus factor

rhesus factor an antigen occurring on the red blood cells of many humans (around 85 per cent) and some other primates. It is particularly important as a cause of haemolytic disease of the newborn and of incompatibility in blood transfusions. It was named in the 1940s for the rhesus monkey in which the antigen was first observed.

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Rh

Rh • abbr. Rhesus (factor). • symb. the chemical element rhodium.

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Rh

Rh, symbol for the element rhodium.

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rhesus factor

rhesus factor: see Rh factor.

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Rh factor

Rh factor n. see rhesus factor.

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Rh factor

Rh factor See RHESUS FACTOR.

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Rh

Rh See rhesus factor.

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Rh

Rhmph, pH, Rh

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Rh Factor

Rh Factor

Definition

Rh (Rhesus) factor is a blood protein that plays a critical role in some pregnancies. People without Rh factor are known as Rh negative, while people with the Rh factor are Rh positive. If a woman who is Rh negative is pregnant with a fetus who is Rh positive, her body may make antibodies against the fetus's blood. This can cause Rh disease in the baby, also known as hemolytic disease of the newborn, or erythroblastosis fetalis. In severe cases, Rh disease leads to brain damage and even death. Since 1968 a vaccine has existed to prevent the mother's body from making antibodies against the fetus's blood.

Description

Rh factor is an antigen found on the red blood cells of most people. Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85% of white Americans and 95% of African-Americans are Rh positive. A person's own health is not affected by the presence or absence of Rh factor.

Rh factor is important only during a pregnancy in which an Rh negative woman is carrying a fetus who might be Rh positive. This can occur when an Rh negative woman conceives a baby with an Rh positive man. The gene for Rh positive blood is dominant over the gene for Rh negative blood, so their baby will be Rh positive. If the Rh positive father also carries the gene for Rh negative blood, his babies have a 50% chance of inheriting Rh negative blood and a 50% chance of inheriting Rh positive blood. If both parents are Rh negative, their babies will always be Rh negative. In order to protect their future babies from Rh disease, all women of childbearing age should know their Rh status before becoming pregnant.

Role in human health

Rh factor in pregnancy

The danger of Rh disease begins when the mother's Rh negative blood is exposed to the baby's Rh positive blood. This mixing of blood can occur at the time of birth, and after an abortion or miscarriage. It may also happen during prenatal tests such as amniocentesis and chorionic villus sampling. More rarely, blood from the mother and fetus may mingle during pregnancy, before birth. When this contact occurs, the mother's body responds by building antibodies to fight the foreign Rh blood protein. The mother's blood is now said to be "sensitized" against Rh factor blood.

Common diseases and disorders

Rh incompatibility

Once a mother's blood has become sensitized, her antibodies will attack the blood of any Rh positive fetus that she carries. The antibodies will destroy the fetus's red blood cells. If this happens, the infant will suffer from Rh factor incompatibility. It will become anemic, a condition caused by a reduction in red blood cells and marked by weakness and fatigue. Severe anemia can lead to heart failure and death. The break-down of red blood cells will also cause the formation of a reddish-yellow substance known as bilirubin. An infant with high levels of bilirubin will look yellowish. This is known as jaundice. Brain damage can occur if the bilirubin level gets high enough. However, Rh incompatibility occurs in varying degrees of severity, with brain damage at the far end of a spectrum.

Rh disease is usually not a problem during a first pregnancy. This is because the Rh negative mother probably will not become sensitized until her blood mixes with the baby's blood during birth. Her baby will be born before her blood can produce antibodies against the baby's Rh positive blood. Once a mother is sensitized, however, any future babies with Rh positive blood will be at risk for Rh disease.

PREVENTION AND TREATMENT. Since 1968 a vaccine has existed to prevent sensitization from occurring. This is the best way to eliminate Rh disease. Available as an injection, the vaccine is called Rh immune globulin (brand name RhoGAM). It blocks the action of the antibodies and prevents the mother's blood from attacking the baby's blood. To be effective, the vaccine must be given any time fetal blood mixes with maternal blood: after birth, abortion, miscarriage, or prenatal tests like amniocentesis and chorionic villus sampling. The vaccine is typically given within 72 hours of any of these events. Since mixing of the blood may also occur during the last three months of pregnancy, the vaccine is also administered at 28 weeks of pregnancy.

A pregnant woman who has already been sensitized from a previous pregnancy will want her doctor to carefully monitor the level of antibodies in her blood throughout her pregnancy. As long as the antibody levels remain relatively low, no problem exists. But if those levels rise, the fetus will need special attention. High antibody levels mean that the fetus's red blood cells are being attacked and destroyed.

KEY TERMS

Amniocentesis— A procedure in which a sample of the fluid in the amniotic sac is removed with a needle for genetic testing.

Antigen— A substance, usually a protein or carbohydrate, that stimulates a response from the immune system.

Bilirubin— Reddish-yellow substance formed by the breakdown of red blood cells.

Chorionic villus sampling— A procedure in which a sample of the membrane surrounding the fetus is taken for genetic testing.

Prenatal test— Procedure done to determine the presence of disease or defect in a fetus.

Sensitization— Occurs when a mother's blood produces antibodies against the blood of her Rh positive fetus.

A fetus whose red blood cells are being destroyed will need a blood transfusion while it is still in the uterus. Two or three transfusions may be necessary before the baby is born. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early, either by inducing birth or by cesarean section. The baby will then receive a transfusion after birth.

ELIMINATING RH DISEASE. Until the introduction of the Rh immune globulin vaccine, Rh disease could not be prevented. About 45 babies per 10,000 births developed the disease each year before widespread use of the vaccine in the early 1970s. Use of the Rh immune globulin vaccine has reduced the chances of the mother becoming sensitized from approximately 12-13% to 1-2%.

Nevertheless, the disease is not completely eradicated. Further steps must be taken, since this is a preventable disease. The majority of cases of Rh disease are the result of women not receiving the vaccine at the appropriate time. Poor women without health insurance, who are likely to lack adequate prenatal care, are especially vulnerable to this oversight. Older women may have become sensitized before the vaccine was available; foreign-born women may not have had access to the vaccine.

Resources

PERIODICALS

Salem, Leon. "Rh incompatibility." eMedicine Journal 2 (May 16, 2001): 〈http://www.emedicine.com/emerg/topic507.htm〉.

OTHER

"Rh Factor and Pregnancy." University of Michigan Health System Website. 1999. July 9, 2001. 〈http://www.smartmoms.org/prenatal-tests/test8.html〉.

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Rh Factor

Rh Factor

Importance of the Rh factor

Rh factor in pregnancy

Treatment for Rh disease

Resources

Rh factor (or Rhesus factor) refers to the Rh D antigen within the five main rhesus antigens of C, c, D, E, and e; what is called the Rhesus system. It is a blood protein that plays a critical role in some pregnancies. People without Rh factor are known as Rh negative, while people with the Rh factor are Rh positive. If a woman who is Rh negative is pregnant with a fetus who is Rh positive, her body will make antibodies against the fetuss blood. This can cause Rh disease, also known as hemolytic disease of the newborn, in the baby. In severe cases, Rh disease leads to brain damage and even death. American pathologist Alexander Solomon Wiener (19071976) and Austrian-American biologist and physician Karl Landsteiner (18681943) named the term Rh factor after they discovered it in the blood of rhesus monkeys in 1937. Since 1968, a vaccine has existed to prevent the mothers body from making antibodies against the fetuss blood.

Importance of the Rh factor

Rh factor is an antigen found on the red blood cells of most people. Rh factor, like the blood types A, B, and O, is inherited from ones parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85% of white Americans and 95% of African Americans are Rh positive. A persons own health is not affected by the presence or absence of Rh factor.

Rh factor is important only during a pregnancy in which an Rh negative woman is carrying a fetus who might be Rh positive. This can occur when an Rh negative woman conceives a baby with an Rh positive man. The gene for Rh positive blood is dominant over the gene for Rh negative blood, so their baby will be Rh positive. If the Rh positive father also carries the gene for Rh negative blood, his babies have a 50% chance of inheriting Rh negative blood and a 50% chance of inheriting Rh positive blood. If both parents are Rh negative, their babies will always be Rh negative. In order to protect their future babies from Rh disease, all women of childbearing age should know their Rh status before becoming pregnant.

Rh factor in pregnancy

The danger of Rh disease begins when the moth-ers Rh negative blood is exposed to the babys Rh positive blood. This mixing of blood occurs at the time of birth, and after an abortion or miscarriage. It is also apt to happen during prenatal tests like amniocentesis and chorionic villus sampling. More rarely, blood from the mother and fetus may mingle during pregnancy, before birth. When this contact between the two blood types occurs, the mothers body responds by building antibodies to fight the foreign Rh blood protein. The mothers blood is now said to be sensitized against Rh factor blood.

Once a mothers blood has become sensitized, her antibodies will attack the blood of any Rh positive fetus that she carries. The antibodies will destroy the fetuss red blood cells. If this happens, the infant will suffer from several serious conditions. It will become

anemic, a condition caused by a reduction in red blood cells and marked by weakness and fatigue. Severe anemia can lead to heart failure and death. The breakdown of red blood cells will also cause the formation of a reddish-yellow substance known as bilirubin. An infant with high levels of bilirubin will look yellowish. This is known as jaundice. Brain damage can occur if the bilirubin level gets high enough. The disease caused by Rh incompatibility is called Rh disease, also known as hemolytic disease of the newborn or erythroblastosis fetalis.

Rh disease is usually not a problem during a first pregnancy. This is because the Rh negative mother probably will not become sensitized until her blood mixes with the babys blood during birth. Her baby will be born before her blood can produce antibodies against the babys Rh positive blood. Once a mother is sensitized, however, any future babies with Rh positive blood will be at risk for Rh disease.

Since 1968, a vaccine has existed to prevent sensitization from ever occurring. This is the best way to eliminate Rh disease. Available as an injection, the vaccine is called Rh immune globulin (brand name RhoGAM). It blocks the action of the antibodies and prevents the mothers blood from attacking the babys blood. To be effective, the vaccine must be given any time fetal blood mixes with maternal blood: after birth, abortion, miscarriage, or prenatal tests like amniocentesis and chorionic villus sampling. The vaccine is typically given within 72 hours of any of these events. Since mixing of the blood may occur during the last three months of pregnancy, some health care providers recommend receiving the vaccine at 28 weeks of pregnancy.

Treatment for Rh disease

If a woman has become sensitized during a previous pregnancy, she can still take steps to prevent future babies who are Rh positive from developing Rh disease. Unfortunately, once a woman has the harmful antibodies in her blood, there is no way to remove them.

A pregnant woman who has already been sensitized from a previous pregnancy will want her doctor to carefully monitor the level of antibodies in her blood throughout her pregnancy. As long as the antibody levels remain relatively low, no problem exists. However, if those levels rise, the fetus will need special attention. High antibody levels mean that the fetus red blood cells are being attacked and destroyed.

A fetus whose red blood cells are being destroyed will need a blood transfusion while it is still in the uterus. Two or three transfusions may be necessary before the baby is born. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early, either through an induced birth or with a cesarean section. The baby will then receive a transfusion after birth.

Eliminating Rh disease Until the introduction of the Rh immune globulin vaccine, Rh disease could not be prevented. About 45 babies per 10,000 births developed the disease each year before widespread use of the vaccine began in the early 1970s. The number of newborns with Rh disease has dropped dramatically since the introduction of the vaccine: to less than 10 per 10,000 in the early 2000s. The prevention of Rh disease is one of the triumphs of modern medicine.

Nevertheless, the number of newborns born in the United States each year with Rh disease is still relatively high. The disease is not completely eradicated. Further steps must be taken, since this is a preventable disease. The majority of cases of Rh disease are the result of women not receiving the vaccine at the appropriate time. Poor women without health insurance, who are likely to lack adequate prenatal care, are especially vulnerable to this oversight. Older women may have become sensitized before the vaccine was available. Foreign-born women may not have had access to the vaccine. With further diligence, health care providers hope to eradicate Rh disease.

See also Antibody and antigen.

KEY TERMS

Bilirubin A yellow pigment that is the end result of hemoglobin degradation. Bilirubin is cleared from the blood by action of liver enzymes and excreted from the body.

Prenatal test Procedure done to determine the presence of disease or defect in a fetus.

Sensitization Occurs when a mothers blood produces antibodies against the blood of her Rh positive fetus.

Resources

BOOKS

Gilbert, Elizabeth Stenn. Manual of High Risk Pregnancy and Delivery. St. Louis, MO: Mosby, 2003.

Johnston, Peter G.B. The Newborn Child. Edinburgh, UK, and New York: Churchill Livingstone, 2003.

Thureen, Patti J. ed. Assessment and Care of the Well Newborn. St. Louis, MO: Elsevier Saunders, 2005.

Zimmerman, David R. Rh: he Intimate History of a Disease and its Conquest. New York: Macmillan, 1973.

Liz Marshall

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Rh Factor

Rh factor

Rh factor is a blood protein that plays a critical role in some pregnancies. People without Rh factor are known as Rh negative , while people with the Rh factor are Rh positive. If a woman who is Rh negative is pregnant with a fetus who is Rh positive, her body will make antibodies against the fetus's blood. This can cause Rh disease , also known as hemolytic disease of the newborn, in the baby. In severe cases, Rh disease leads to brain damage and even death. Since 1968, a vaccine has existed to prevent the mother's body from making anti-bodies against the fetus's blood.

Importance of the Rh factor

Rh factor is an antigen found on the red blood cells of most people. Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85% of white Americans and 95% of African Americans are Rh positive. A person's own health is not affected by the presence or absence of Rh factor.

Rh factor is important only during a pregnancy in which an Rh negative woman is carrying a fetus who might be Rh positive. This can occur when an Rh negative woman conceives a baby with an Rh positive man. The gene for Rh positive blood is dominant over the gene for Rh negative blood, so their baby will be Rh positive. If the Rh positive father also carries the gene for Rh negative blood, his babies have a 50% chance of inheriting Rh negative blood and a 50% chance of inheriting Rh positive blood. If both parents are Rh negative, their babies will always be Rh negative. In order to protect their future babies from Rh disease, all women of childbearing age should know their Rh status before becoming pregnant.


Rh factor in pregnancy

The danger of Rh disease begins when the mother's Rh negative blood is exposed to the baby's Rh positive blood. This mixing of blood occurs at the time of birth , and after an abortion or miscarriage. It is also apt to happen during prenatal tests like amniocentesis and chorionic villus sampling. More rarely, blood from the mother and fetus may mingle during pregnancy, before birth. When this contact between the two blood types occurs, the mother's body responds by building antibodies to fight the foreign Rh blood protein. The mother's blood is now said to be "sensitized" against Rh factor blood.

Once a mother's blood has become sensitized, her antibodies will attack the blood of any Rh positive fetus that she carries. The antibodies will destroy the fetus's red blood cells. If this happens, the infant will suffer from several serious conditions. It will become anemic, a condition caused by a reduction in red blood cells and marked by weakness and fatigue. Severe anemia can lead to heart failure and death. The breakdown of red blood cells will also cause the formation of a reddish-yellow substance known as bilirubin. An infant with high levels of bilirubin will look yellowish. This is known as jaundice . Brain damage can occur if the bilirubin level gets high enough. The disease caused by Rh incompatibility is called Rh disease, also known as hemolytic disease of the newborn or erythroblastosis fetalis.

Rh disease is usually not a problem during a first pregnancy. This is because the Rh negative mother probably will not become sensitized until her blood mixes with the baby's blood during birth. Her baby will be born before her blood can produce antibodies against the baby's Rh positive blood. Once a mother is sensitized, however, any future babies with Rh positive blood will be at risk for Rh disease.

Since 1968, a vaccine has existed to prevent sensitization from ever occurring. This is the best way to eliminate Rh disease. Available as an injection, the vaccine is called Rh immune globulin (brand name RhoGAM). It blocks the action of the antibodies and prevents the mother's blood from attacking the baby's blood. To be effective, the vaccine must be given any time fetal blood mixes with maternal blood: after birth, abortion, miscarriage, or prenatal tests like amniocentesis and chorionic villus sampling. The vaccine is typically given within 72 hours of any of these events. Since mixing of the blood may occur during the last three months of pregnancy, some health care providers recommend receiving the vaccine at 28 weeks of pregnancy.

Treatment for Rh disease

If a woman has become sensitized during a previous pregnancy, she can still take steps to prevent future babies who are Rh positive from developing Rh disease. Unfortunately, once a woman has the harmful antibodies in her blood, there is no way to remove them.

A pregnant woman who has already been sensitized from a previous pregnancy will want her doctor to carefully monitor the level of antibodies in her blood throughout her pregnancy. As long as the antibody levels remain relatively low, no problem exists. But if those levels rise, the fetus will need special attention. High antibody levels mean that the fetus's red blood cells are being attacked and destroyed.

A fetus whose red blood cells are being destroyed will need a blood transfusion while it is still in the uterus. Two or three transfusions may be necessary before the baby is born. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early, either through an induced birth or with a cesarean section. The baby will then receive a transfusion after birth.


Eliminating Rh disease

Until the introduction of the Rh immune globulin vaccine, Rh disease could not be prevented. About 45 babies per 10,000 births developed the disease each year before widespread use of the vaccine in the early 1970s. The number of newborns with Rh disease has dropped dramatically since the introduction of the vaccine, to about 10 per 10,000 in the early 1990s. The prevention of Rh disease is one of the triumphs of modern medicine.

Nevertheless, the number of newborns born in the United States each year with Rh disease is still relatively high. The disease is not completely eradicated. Further steps must be taken, since this is a preventable disease. The majority of cases of Rh disease are the result of women not receiving the vaccine at the appropriate time. Poor women without health insurance, who are likely to lack adequate prenatal care, are especially vulnerable to this oversight. Older women may have become sensitized before the vaccine was available. Foreign-born women may not have had access to the vaccine. With further diligence, health care providers hope to eradicate Rh disease.

See also Antibody and antigen.


Resources

books

Reuben, Carolyn. The Health Baby Book. New York: Jeremy P. Tarcher/Perigee Books, 1992.

Rich, Laurie A. When Pregnancy Isn't Perfect. New York: Dutton, 1991.

periodicals

Heins, Henry C. "Should You Worry About Rh Disease?" American Baby (April 1992): 24.

other

March of Dimes Public Health Education Information Sheet Planning for Pregnancy, Birth, and Beyond. Washington, DC: American College of Obstetricians and Gynecologists, 1990.


Liz Marshall

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bilirubin

—A yellow pigment that is the end result of hemoglobin degradation. Bilirubin is cleared from the blood by action of liver enzymes and excreted from the body.

Prenatal test

—Procedure done to determine the presence of disease or defect in a fetus.

Sensitization

—Occurs when a mother's blood produces antibodies against the blood of her Rh positive fetus.

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Rh Factor

Rh Factor


Rh factor describes a certain blood-type marker that each human blood type either has (Rh-positive) or does not have (Rh-negative). As a further refinement of determining exactly what blood type a person is, the Rh factor is important not only for proper blood transfusions but also during pregnancy.

In 1909 the Austrian physician, Karl Landsteiner (1868–1943), explained why blood cells agglutinate, or clump, together when blood from different people were mixed. He showed that all human blood can be divided into four main groups, some of which are compatible and many which are not. He named these four groups blood type A, type B, type AB, and type O according to the particular type of antigen they had on their red blood cells. (An antigen is a protein that works as a type of chemical identification tag.) People from the same blood type could exchange their blood, but those with different blood types had to follow certain exact rules if they were to successfully receive a blood transfusion.

Overall, Landsteiner's discovery made blood transfusions fairly safe and saved many a life. However, despite his breakthrough in understanding blood types, there continued to be enough unexplained accidents during blood transfusions to send Landsteiner searching for the possibility that some other factor might exist that was yet unknown. By 1940, Landsteiner and his associates discovered a different factor in the blood of rhesus monkeys, and he later found that this factor also existed in human blood. As with the four major human blood types, each of which had (or did not have) a certain, specific type of antigen, certain human blood also was found to have an antigen that he named antigen D. If blood had this antigen, it was therefore Rh-positive. Those without the antigen were considered Rh-negative. The symbol Rh was used as an abbreviation for Rhesus. Studies have since shown that about 85 percent of the population are Rh-positive and 15 percent are Rh-negative.

Blood type, like a person's Rh factor, is inherited. The Rh factor only becomes important when a person receives a blood transfusion or when a woman is pregnant. If a person who is Rh-negative receives blood from an Rh-positive person, then the Rh-negative blood will produce antibodies against the Rh-positive factor. Antibodies are proteins in the plasma (the liquid part of the blood) that destroy foreign substances. Therefore, the next time that person's system encounters Rh-positive blood, it will cause what is called a hemolytic reaction and make the blood agglutinate together. This can cause serious injury or death to the patient.

The Rh factor is also critical during pregnancy. If an Rh-negative woman gives birth to an Rh-positive child whose father was RH-positive, there is a risk that her system will become sensitized to her baby's Rh factor and will begin to produce Rh-positive antibodies. While her first baby usually will not be affected, her next child may be in danger since the mother's system may send antibodies into the child's bloodstream while she is still carrying the fetus. This could threaten the child's life. This condition is known as erythroblastosis fetalis, or hemolytic disease of the newborn (HDN). It can cause severe anemia (lack of hemoglobin or red blood cells), brain damage, or even death.

Before the Rh factor became known, it was a major cause of stillbirth pregnancies (when the baby is born dead). Today, this situation can be prevented. At twenty-eight weeks into her pregnancy and immediately after birth, the mother can be given an injection that destroys any Rh-positive antibodies she has in her system. Also, the baby can be given a blood transfusion just before birth while it is still in the womb, or immediately after it is born. A check of blood type and Rh factor are now routine in all blood transfusions and pregnancies.

[See alsoAntibody and Antigen; Blood; Blood Types ]

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