Rh incompatibility occurs when a pregnant individual has Rh-negative blood and the fetus has Rh-positive blood. While it can lead to serious complications, including miscarriage, it is often preventable and manageable with medical care. Early identification and intervention are key to ensuring positive outcomes for the pregnant person and the baby.
Understanding the Rh Factor
The Rh factor is a protein found on the surface of red blood cells. Individuals who possess this protein are considered Rh-positive, while those who do not are Rh-negative. This factor is inherited from parents, independent of ABO blood type.
A person’s Rh status is determined by inherited genes. An Rh-positive status is dominant, meaning one inherited Rh-positive gene makes a person Rh-positive. To be Rh-negative, a person must inherit two Rh-negative genes. This explains how an Rh-negative mother can conceive an Rh-positive baby if the father is Rh-positive.
How Rh Incompatibility Impacts Pregnancy
Rh incompatibility becomes a concern when an Rh-negative mother is exposed to Rh-positive fetal blood, leading to an immune response known as sensitization. This exposure can occur during various events such as delivery, miscarriage, abortion, certain prenatal procedures, or abdominal trauma. Upon exposure, the mother’s immune system identifies the Rh-positive fetal blood cells as foreign and produces antibodies against them.
These antibodies can cross the placenta in subsequent Rh-positive pregnancies. Once in the fetal bloodstream, these maternal antibodies attack and destroy the baby’s Rh-positive blood cells, leading to hemolytic disease of the fetus and newborn (HDFN). HDFN can cause fetal anemia, where red blood cells are destroyed faster than replaced, potentially leading to a lack of oxygen. In severe cases, HDFN can result in hydrops fetalis, a condition characterized by fluid retention and organ damage, potentially leading to fetal death, miscarriage, or stillbirth. The condition’s severity often increases with each subsequent Rh-positive pregnancy if the mother becomes sensitized.
Preventing and Managing Rh Incompatibility
Preventing Rh incompatibility relies on early detection and intervention during prenatal care. All pregnant individuals undergo blood tests to determine their Rh status. If an individual is found to be Rh-negative, further testing may be done on the father to assess the risk of the baby being Rh-positive.
The primary preventive measure is the administration of Rho(D) immune globulin (RhoGAM). This injection contains antibodies that temporarily prevent the Rh-negative mother’s immune system from producing its own antibodies against Rh-positive fetal blood cells. RhoGAM is typically administered around 28 weeks of pregnancy and again within 72 hours after the birth of an Rh-positive baby. It is also given after any event that could cause maternal-fetal blood mixing, such as miscarriage, abortion, ectopic pregnancy, or invasive prenatal procedures.
For pregnancies where sensitization has already occurred, monitoring strategies include regular antibody titer tests to measure Rh antibodies and ultrasounds to assess the fetus for signs of anemia. If severe HDFN is diagnosed, treatment options for the fetus before birth can include intrauterine blood transfusions, where Rh-negative blood is transfused into the baby’s umbilical cord. After birth, affected newborns may receive phototherapy for jaundice, intravenous immunoglobulin to reduce red blood cell destruction, or exchange transfusions in severe cases to replace affected blood with healthy Rh-negative blood. These interventions aim to mitigate the effects of HDFN and improve outcomes for the baby.