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Rhesus (Rh) factor is a specific protein that is found on the surface of red blood cells. Individuals with the Rh factor are considered Rh-positive. Approximately 85% of the population is Rh positive. Those without the Rh factor are Rh-negative. Rh factor typically does not cause health concerns. However, Rh factor can cause life-threatening complications during pregnancy if the mother is Rh-negative and the fetus is Rh-positive from the father’s genetics.

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Rh Factor Risks

Typically, a woman’s first pregnancy does not present serious risks of Rh factor complications. During the second or later pregnancy, complications can occur if a mother’s Rh-negative blood comes in contact with a fetus’ Rh factor blood. When the blood mixes, the mother develops antibodies to the Rh factor of the fetus. Antibodies are protein molecules that work to destroy foreign substances inside the blood. This process is similar to an allergic reaction. It is referred to as sensitization.

Situations that can cause maternal sensitization to the Rh factor include:

  • Miscarriage
  • Ectopic pregnancy
  • Blood transfusion
  • Bleeding during pregnancy
  • Blunt trauma during pregnancy
  • Induced abortion or menstrual extraction
  • Rotation of the fetus during delivery
  • Tubal ligation, or “tying” of the Fallopian tubes
  • Amniocentesis, or a prenatal test requiring a sample of the amniotic fluid
  • Chorionic villus sampling, or a prenatal test requiring a sample of part of the placenta

Rh Factor Complications

The sensitized mother’s antibodies can cross over the placenta and attack the blood of the fetus. These antibodies begin to break down and rupture the fetal Rh factor red blood cells. This causes anemia, or a low red blood cell count in the blood. This condition is referred to as hemolytic anemia or hemolytic disease.

Hemolytic anemia in a fetus can lead to:

  • Brain damage
  • Jaundice
  • Severe anemia
  • Pulmonary hypertension
  • Heart failure
  • Death

Diagnosis and Treatment

When a pregnancy is confirmed, a blood test should be among the first tests performed on the mother. Blood testing is used to determine the mother’s blood type and Rh factor. If the mother does not have the Rh factor and the fetus does, medical professionals should administer Rh immunoglobulin. One Rh immunoglobulin injection is given around 28 weeks gestation. Another is given within 72 hours of giving birth. The injections act as a vaccine to prevent the mother’s blood from developing antibodies.

Early detection and treatment of Rh factor incompatibility is crucial to a healthy pregnancy. Rh immunoglobulin injections cannot be given after the mother’s blood has already begun producing antibodies. An antibody screen is used to test for antibodies in the blood. Once the mother is sensitized and antibodies are present, the pregnancy must be monitored closely to prevent potential harm to the fetus.

If the Rh factor incompatibility is severe, the fetus may require a series of blood exchange transfusions before or after delivery. These transfusions replace the fetal red blood cells with Rh-negative cells. This transfusion stabilizes the fetal blood and minimizes potential damage from antibodies that have already entered the fetus’ bloodstream.



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