The Rh factor is a protein found on red blood cells. Individuals are Rh-positive if they have it, or Rh-negative if they don’t. A common concern is whether an Rh mismatch between a mother and baby can cause miscarriage. This article explains the link between Rh-negativity and pregnancy outcomes.
Understanding Rh Factor
The Rh factor, also known as the Rhesus factor, is an inherited protein. Individuals are classified as Rh-positive if they possess this protein or Rh-negative if it is absent. Approximately 85% of people are Rh-positive, making it the more common status. A baby inherits their Rh factor from their parents, meaning it is genetically determined. If both parents are Rh-negative, their child will also be Rh-negative. If one parent is Rh-positive and the other is Rh-negative, or if both are Rh-positive, the child can be either Rh-positive or Rh-negative depending on the genetic combination.
How Rh Incompatibility Develops
Rh incompatibility arises when an Rh-negative mother carries an Rh-positive fetus. During pregnancy or delivery, fetal red blood cells can enter the mother’s bloodstream. The mother’s immune system recognizes these cells as foreign and begins to produce antibodies against the Rh-positive protein, a process known as Rh sensitization or alloimmunization. Sensitization typically takes time, so the first Rh-positive pregnancy is usually unaffected. However, once these antibodies form, they persist in the mother’s system and can pose a risk to subsequent Rh-positive pregnancies.
Effects on Pregnancy and Fetal Health
Rh incompatibility generally does not cause early miscarriages. The primary concern is Hemolytic Disease of the Fetus and Newborn (HDFN), also called Rh disease. In HDFN, maternal antibodies cross the placenta and target the fetus’s Rh-positive red blood cells. This leads to the breakdown of fetal red blood cells, resulting in anemia. The severity of HDFN can range from mild to severe, potentially causing fetal anemia, jaundice, and an enlarged liver or spleen. In extreme, untreated cases, severe HDFN can lead to hydrops fetalis, stillbirth, or late miscarriage, distinguishing these outcomes from common early pregnancy losses.
Preventing and Treating Rh Incompatibility
Medical advancements have made Rh incompatibility largely preventable and manageable. The main intervention is Rho(D) immune globulin, known as RhoGAM, which prevents the Rh-negative mother’s immune system from producing antibodies when exposed to Rh-positive fetal blood. RhoGAM is typically given to Rh-negative mothers around 28 weeks of pregnancy and again within 72 hours after delivering an Rh-positive baby. It is also administered after events that could mix maternal and fetal blood, such as miscarriage, abortion, ectopic pregnancy, or certain invasive prenatal procedures like amniocentesis. Regular antibody screening throughout pregnancy helps monitor for sensitization, and for cases where sensitization has already occurred, specialized care including close fetal monitoring and intrauterine blood transfusions can help manage HDFN.