The Rh factor is a protein found on the surface of red blood cells. Its presence or absence classifies an individual as either Rh positive or Rh negative. Understanding this factor is important in various biological contexts, particularly concerning human compatibility.
What is the Rh Factor?
The Rh factor, also known as the Rhesus factor, is an inherited protein located on the exterior of red blood cells. If a person’s red blood cells carry this protein, they are classified as Rh positive (Rh+). Conversely, individuals whose red blood cells lack this protein are considered Rh negative (Rh-). This factor is distinct from the ABO blood group system, which classifies blood types as A, B, AB, or O. While the Rh factor does not affect a person’s general health, its status becomes relevant in situations involving blood mixing, such as blood transfusions and pregnancy. Approximately 85% of people are Rh positive, making Rh negative less common.
How Rh Factor is Inherited
The inheritance of the Rh factor follows predictable genetic patterns, directly addressing whether Rh negative is recessive. The Rh positive trait is determined by a dominant gene, while the Rh negative trait is recessive. This means that an individual will be Rh positive if they inherit at least one dominant Rh positive gene from either parent. For a person to be Rh negative, they must inherit two copies of the recessive Rh negative gene, one from each biological parent. If both parents are Rh negative, all their children will also be Rh negative. However, if one or both parents are Rh positive, their children could be either Rh positive or Rh negative, depending on the specific combination of genes inherited.
Rh Factor’s Role in Pregnancy
The Rh factor plays a significant role in pregnancy when there is a difference in Rh status between the mother and the developing fetus. This situation, known as Rh incompatibility, arises when an Rh negative mother carries an Rh positive fetus. Although the mother and fetus do not typically share blood during pregnancy, small amounts of fetal blood can enter the mother’s bloodstream, particularly during events like delivery, miscarriage, or certain prenatal procedures. Upon exposure to Rh positive fetal red blood cells, an Rh negative mother’s immune system may produce antibodies against the Rh factor. These antibodies usually do not affect the first Rh positive pregnancy, as sensitization often occurs during delivery; however, they can cross the placenta in subsequent pregnancies, attacking fetal red blood cells and potentially causing hemolytic disease of the newborn, leading to anemia, jaundice, or other health issues for the baby.
Addressing Rh Incompatibility
Medical management effectively addresses Rh incompatibility to prevent complications. Routine Rh factor testing is a standard part of early prenatal care for all pregnant individuals. This blood test determines the mother’s Rh status and helps identify pregnancies that may be at risk for Rh incompatibility. If an Rh negative mother is identified, and she has not yet developed Rh antibodies, she will typically receive an injection of Rh immune globulin, often known by brand names like RhoGAM. This medication works by preventing the mother’s immune system from forming antibodies against Rh positive blood cells. The injection is commonly administered around 28 weeks of pregnancy and again within 72 hours after delivery if the baby is found to be Rh positive. Additional doses may be given after events such as miscarriage, abortion, or invasive prenatal tests that could lead to blood mixing. This preventive measure has significantly reduced the incidence of Rh incompatibility complications.