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The Rhesus (Rh) factor is a protein found on the surface of the red blood cells (RBCs).
When a woman is Rh-negative and her fetus is Rh-positive (because the father is Rh-positive), the woman’s body might produce proteins called “Rh antibodies” after exposure to the baby's red blood cells that can lead to a problem called “Rh incompatibility.”
Rh incompatibility usually is not a problem in the woman’s first pregnancy because the baby's blood does not normally enter the mother's circulatory system during the pregnancy. But Rh antibodies are a concern or can become harmful during the woman’s second or subsequent pregnancies.
- Rh incompatibility occurs when the blood of an Rh-positive fetus gets into the bloodstream of an Rh-negative woman. Her body recognizes the Rh-positive blood as a foreign substance.
- In response to this, the female body produces anti-Rh antibodies. These antibodies can cross the placenta and attack the fetus’s blood cells, which can lead to serious health problems including:
The risk of complications and severity increases steadily with subsequent pregnancies.
What is the Rh factor?
The Rhesus (Rh) factor is a protein found on the surface of the red blood cells (RBCs). The presence of this protein on the RBCs means you are Rh-positive, whereas the absence of this protein marks you to be Rh-negative.
Rh-positive is the most common blood type; however, an Rh-negative blood type is not an illness and does not cause any harm to the health other than needing special care if an Rh-negative woman carries an Rh-positive baby.
The Rh factor is inherited (passed from parent to child through genes) to the fetus from the father or the mother.
Theoretically, around half of the children born to Rh-negative mother and Rh-positive father will be Rh-positive leading to Rh incompatibility.
How do Rh antibodies develop?
During pregnancy, a woman and her fetus usually do not share blood; however, in some cases, a small amount of blood from the fetus can mix with the woman’s blood which can happen during labor and birth or else during:
- Amniocentesis (a prenatal test wherein a sample of the amniotic fluid is removed for testing or treatment)
- Chorionic villus sampling (a prenatal test wherein a sample of the chorionic villi [wispy projections of the placenta] is removed for testing)
- Bleeding during pregnancy
- Cordocentesis (a diagnostic prenatal test wherein a sample of the baby's blood is taken from the umbilical cord for testing)
- Attempts to manually turn a fetus in breech presentation
- Trauma to the abdomen during pregnancy
- Removal of molar pregnancy (a noncancerous uterine tumor)
- Generally, if the blood from mother and child mixes during delivery in the first pregnancy, the baby escapes the complications. The next baby (if Rh negative) may face complications only if the blood of the baby and mother mixes (which is not normal).
An Rh-negative mother might need to have another blood test, an antibody screening, that is used to detect antibodies to Rh-positive blood, during the first trimester, during Week 28 of pregnancy, and at delivery.
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The first sign of pregnancy is most often:
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How do Rh antibodies affect pregnancy?
first pregnancy because her body does not have a chance to develop enough antibodies at that time, but if treatment is not given during the first pregnancy and the woman gets pregnant again with an Rh-positive fetus, her body has sufficient antibodies enough to put a future fetus at risk.
An Rh-negative woman can also make antibodies after:
- Miscarriage
- Ectopic pregnancy
- Induced abortion
- Procedures during pregnancy such as the eternal cephalic version to position a breech baby in a head-first position
- Invasive procedures such as chorionic villi sampling and trauma.
Can Rh incompatibility be prevented?
Yes, problems caused by Rh incompatibility during pregnancy can be prevented.
Treatment can be given to prevent these problems aiming to stop an Rh-negative woman from making Rh antibodies in the first place.
This can be done by finding out if the woman is Rh negative early in pregnancy (or before pregnancy) and, if needed, giving a medication to prevent antibodies from forming.
The obstetric care providers may request tests during the first trimester of an Rh-negative woman and then again at 28 weeks of pregnancy.
Depending on the antibody screening and antibody production, an injection of Rh immune globulin can be given.
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Rh factor chart
Rh-positive
Rh-positive
Rh-positive
None
Rh-negative
Rh-negative
Rh-negative
None
Rh-positive
Rh-negative
Rh-positive or Rh-negative
None
Rh-negative
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Rh-positive or Rh-negative
Rh immune globulin injections are mandatory
How is Rh incompatibility treated?
For a pregnant woman who has the potential to develop Rh incompatibility, a series of two Rh immune globulin shots are given during her first pregnancy. Rh immune globulin (Rhlg) is a medication (acts like a vaccine) that stops the body from making antibodies that can prevent severe fetal anemia in a future pregnancy.
- First shot: around the 28th week of pregnancy
- Second shot: within 72 hours of giving birth
An Rh-negative woman also might get a dose of RhIg if she has a miscarriage, an amniocentesis, or any bleeding during the pregnancy.
In some cases, if a woman has already developed Rh antibodies, her pregnancy will be closely watched to make sure that antibody levels are not too high.
In rare cases, if the incompatibility is severe and the baby is in danger, the baby can get specialized blood transfusions called exchange transfusions either before birth (intrauterine fetal transfusions) or after delivery.
Exchange transfusions are a procedure to replace the baby's blood with Rh-negative blood cells that stabilizes the level of red blood cells and minimizes the damage from Rh antibodies already in the baby's bloodstream.