Rh factor is a protein found on the surface of red blood cells. Its presence makes an individual Rh-positive, while its absence makes them Rh-negative. Most people, about 85%, are Rh-positive. Rh incompatibility, also known as Rh disease or Hemolytic Disease of the Fetus and Newborn (HDFN), occurs when an Rh-negative pregnant individual carries an Rh-positive baby. This can lead to medical complications for the baby.
Understanding Rh Factor
The Rh factor is an inherited protein, passed down from biological parents. Blood types are classified not only by ABO groups but also by the presence or absence of this Rh protein. Being Rh-negative is not a health problem on its own; it does not cause illness or affect a person’s general well-being. However, this factor becomes medically significant during pregnancy, especially when there is a difference in Rh status between the pregnant individual and the baby.
Rh Incompatibility and Its Impact
The baby can inherit the Rh-positive factor from an Rh-positive biological father. Although blood typically does not mix between the pregnant individual and the baby during pregnancy, small amounts of fetal blood can enter the maternal circulation, particularly during events like delivery, miscarriage, or certain prenatal procedures.
When an Rh-negative individual is exposed to Rh-positive blood, their immune system may recognize the Rh protein as foreign. In response, the body produces antibodies against the Rh factor, a process called sensitization. These antibodies, specifically IgG antibodies, can then cross the placenta in subsequent pregnancies. If a later pregnancy involves another Rh-positive baby, these maternal antibodies can attack and destroy the baby’s red blood cells, leading to Rh disease.
Recognizing Signs of Rh Disease in Infants
Signs of Rh disease can be observed before birth through specialized imaging. An ultrasound might reveal:
- An enlarged liver, spleen, or heart in the fetus.
- Fluid accumulation in various parts of the baby’s body, such as the abdomen, around the heart, or lungs (hydrops fetalis).
- Excess amniotic fluid (polyhydramnios).
- Yellow coloring of the amniotic fluid due to bilirubin buildup.
After birth, several signs may indicate Rh disease. Jaundice, characterized by yellowing of the skin and the whites of the eyes, is common. This occurs because the rapid breakdown of red blood cells produces an excess of bilirubin, which the baby’s immature liver struggles to process. Anemia is another sign, leading to paleness, lethargy, and potentially rapid breathing or a fast heart rate as the baby’s body attempts to compensate for the lack of oxygen-carrying red blood cells. Swelling under the skin or an enlarged abdomen due to an enlarged spleen or liver can also be observed. In severe cases, high bilirubin levels can lead to kernicterus, which can cause brain damage.
Diagnosis and Management of Rh Incompatibility
Diagnosis of Rh incompatibility begins early in pregnancy with a blood test for the pregnant individual to determine their Rh factor. If the individual is Rh-negative, the partner may also be tested. An antibody screen, often called an indirect Coombs test, is performed to check for the presence of Rh antibodies in the maternal blood.
If Rh antibodies are detected or if the baby is at risk, further monitoring may involve prenatal ultrasounds to assess for signs like fluid buildup or organ enlargement. More invasive tests such as amniocentesis or cordocentesis (sampling of the baby’s blood from the umbilical cord) may be performed to check the baby’s Rh status, bilirubin levels, and signs of anemia. After birth, the baby’s blood will be tested, often including a direct Coombs test, to identify maternal antibodies attached to the baby’s red blood cells. Management of Rh disease can range from close monitoring to intrauterine blood transfusions for severe anemia in the fetus or early delivery.
Preventing Rh Incompatibility
Preventing Rh incompatibility is effective with the use of Rh immunoglobulin. This medication contains antibodies that help prevent an Rh-negative individual’s immune system from becoming sensitized to Rh-positive blood.
Rh-negative pregnant individuals receive an injection of Rh immunoglobulin around 26 to 28 weeks of pregnancy. A second dose is given within 72 hours after delivering an Rh-positive baby. Rh immunoglobulin is also administered after events that could lead to mixing of maternal and fetal blood, such as miscarriage, abortion, ectopic pregnancy, abdominal trauma, or certain invasive prenatal procedures like amniocentesis. This preventive measure has reduced the incidence of severe Rh disease, protecting future pregnancies.