The Rh factor is a protein found on the surface of red blood cells. Its presence makes an individual Rh-positive; its absence makes them Rh-negative. While generally not a health concern, the Rh factor becomes medically relevant, especially during pregnancy.
Understanding Rh Factor Basics
The Rh factor (Rhesus factor) is an inherited protein on the surface of red blood cells. Your blood is Rh-positive if the protein is present, or Rh-negative if absent. The positive or negative sign next to your blood type, like A+ or O-, indicates your Rh status.
About 85% of people are Rh-positive, making Rh-negative blood types less common. This genetic trait passes from parents to children, with each parent contributing one gene. The Rh-positive gene is dominant; inheriting at least one makes a person Rh-positive. This determines Rh status, separate from ABO blood group.
How to Determine Your Rh Status
Your Rh status is determined by a simple blood test, often called a type and screen. This test identifies the presence of the Rh protein on your red blood cells and requires no special preparation. Healthcare providers perform Rh factor tests in several medical scenarios. For pregnant individuals, it is routinely conducted during the first prenatal visit to assess potential Rh incompatibility. It is also common before blood transfusions or organ donations to ensure compatibility and prevent adverse reactions.
Being Rh Negative and Pregnancy
Being Rh-negative typically does not affect your health, but it is important during pregnancy if the baby is Rh-positive. This situation, known as Rh incompatibility, occurs when an Rh-negative mother carries an Rh-positive fetus. A baby inherits its Rh factor from its parents. If the father is Rh-positive, there is a chance the baby will also be Rh-positive (approximately 50% if the father is heterozygous).
During pregnancy, a small amount of the baby’s blood can mix with the mother’s, especially during delivery. Mixing can also occur during procedures like amniocentesis or chorionic villus sampling, abdominal trauma, vaginal bleeding, or miscarriage. If Rh-positive fetal blood enters the Rh-negative mother’s bloodstream, her immune system may identify the Rh protein as foreign.
In response, the mother’s body can produce antibodies against the Rh protein, a process called Rh sensitization. Sensitization usually does not affect the first Rh-positive pregnancy because antibody production takes time, and exposure often happens during delivery. Once formed, these antibodies persist in the mother’s system for life. In subsequent Rh-positive pregnancies, these existing maternal antibodies can cross the placenta into the baby’s bloodstream.
These antibodies attack and destroy the baby’s red blood cells, leading to hemolytic disease of the newborn (HDFN). The presence of maternal antibodies against the fetal Rh-positive red blood cells can result in the destruction of those cells faster than the baby’s body can replace them. HDFN can cause severe anemia, jaundice, fluid buildup, and life-threatening complications for the baby, often worsening with each successive Rh-positive pregnancy.
Treatment and Management for Rh Incompatibility
Medical advancements allow effective prevention and management of Rh incompatibility. The primary intervention is an injection of Rh immune globulin, often known by brand names like RhoGAM. This medication is given to Rh-negative mothers to prevent their immune system from producing antibodies against Rh-positive fetal red blood cells.
RhoGAM works by temporarily introducing a small amount of anti-D antibodies into the mother’s system. These antibodies coat any Rh-positive fetal red blood cells that may have entered the mother’s bloodstream, preventing her immune system from recognizing them and forming its own permanent antibodies. This intervention is crucial because once the mother’s body produces its own Rh antibodies, RhoGAM is no longer effective in preventing sensitization.
RhoGAM is typically administered around 26 to 28 weeks of pregnancy and again within 72 hours after delivery if the baby is found to be Rh-positive. It may also be given after events such as miscarriage, abortion, or invasive prenatal tests that could lead to mixing of maternal and fetal blood. The routine use of Rh immune globulin has significantly reduced the occurrence of hemolytic disease of the newborn.