Erythroblastosis fetalis is two potentially disabling or fatal blood disorders in infants: Rh incompatibility disease and ABO incompatibility disease. These disorders are caused by incompatibility between a mother's blood and her unborn baby's blood and may be apparent before birth. Because of the incompatibility, the mother's immune system destroys the baby's blood cells, and the baby suffers severe anemia (deficiency in red blood cells), brain damage, or death. A person's blood type is determined by genes inherited from parents: proteins called antigens in red blood cells and the presence or absence of the Rh-factor. Blood is classified as A, B, AB, or O and positive or negative (e.g., A-positive or B-negative). Blood type doesn't affect health, but the immune system accepts only the individual's blood type or a close match. Introduction of a radically different blood type causes the immune system to produce antibodies that attack and destroy cells carrying the foreign antigen. In a pregnant woman, blood cells from the unborn baby can cross overinto the mother's bloodstream, especially at delivery. If the blood types areincompatible, the mother's immune system makes antibodies against the baby'sblood. Usually, this doesn't happen in a first pregnancy.
Rh incompatibility disease and ABO incompatibility disease have similar symptoms, but Rh disease is much more severe because more of the baby's blood cells are destroyed. Both incompatibility diseases are uncommon in the United States. Rh disease only occurs if a mother is Rh-negative and her baby is Rh-positive, which happens only when the baby inherits the Rh factor gene from thefather. Most people are Rh-positive. ABO incompatibility disease is almost always limited to babies with A or B antigens whose mothers have type O blood.Approximately one third of these babies show evidence of the mother's antibodies in their bloodstream, but only a small percentage develop symptoms of ABOincompatibility disease. The baby's body tries to compensate for the anemiacaused by the mother's antibodies by releasing immature red blood cells, called erythroblasts. The overproduction of erythroblasts can cause the liver andspleen to become enlarged, potentially causing liver damage or a ruptured spleen. Excess erythroblast production means that fewer of other types of bloodcells are produced, such as platelets and other factors important for bloodclotting. Excessive bleeding can be a complication. The destroyed red blood cells release the blood's red pigment (hemoglobin) which degrades into a yellow substance called bilirubin. Bilirubin is normally produced as red blood cells die, but the body can only handle a low level of bilirubin. In erythroblastosis fetalis, high levels of bilirubin accumulate and cause hyperbilirubinemia, a condition in which the baby becomes jaundiced, a yellowish tone of theeyes and skin. If hyperbilirubinemia cannot be controlled, the baby developskernicterus, in which bilirubin is deposited in the brain and may cause permanent damage. Other symptoms include high levels of insulin and low blood sugar, as well as a condition called hydrops fetalis. Hydrops fetalis causes fluids to accumulate within the baby's body, making it look swollen. This inhibits normal breathing and can interfere with lung growth if it continues for anextended period. Hydrops fetalis and anemia can also contribute to heart problems.
Erythroblastosis fetalis can be predicted before birth by determining the mother's blood type. If she is Rh-negative, the father's blood is tested to determine whether he is Rh-positive. If the father is Rh-positive, the mother's blood will be checked for antibodies against the Rh factor. A blood test thatdemonstrates no antibodies is repeated at week 26 or 27 of the pregnancy. Blood incompatibility is uncovered through blood tests such as the Coombs test,and others. When a mother has antibodies against her unborn infant's blood, the antibodies are monitored and if levels increase, amniocentesis, fetal umbilical cord blood sampling, and ultrasound are used to assess any effects on the baby. If the baby is in danger, and the pregnancy is at least 32-34 weeksalong, labor is induced. Under 32 weeks, the baby is given blood transfusions while in the mother's uterus. After birth, the severity of the baby'ssymptoms is assessed. Transfusions may be necessary to treat anemia, hyperbilirubinemia, and bleeding. Hyperbilirubinemia is also treated with phototherapy, oxygen and intravenous fluids, or drugs. Treatment of minor symptoms is typically successful and the baby will not suffer long-term problems. Erythroblastosis is a serious condition for approximately 4,000 babies annually, 15%of whom die before birth. Babies who survive pregnancy may develop kernicterus, which can lead to deafness, speech problems, cerebral palsy, or mental retardation. Extended hydrops fetalis can inhibit lung growth and contribute toheart failure. These serious complications are life threatening, but with good medical treatment, the fatality rate is very low. With any pregnancy, blood typing is a universal precaution against blood incompatibility disease. If an Rh-negative woman gives birth to an Rh-positive baby, she is injected with immunoglobulin G, a type of antibody protein, within 72 hours of the birth, to destroy fetal blood cells in her bloodstream before her immune system can react to them.