The Rh Factor: How It Can Affect Your Pregnancy

The Rh factor is a protein that can be found on the surface of red blood cells. If your blood cells have this protein, you are Rh positive. If your blood cells do not have this protein, you are Rh negative. The "positive" or "negative" part of your blood type, such as O positive or A negative, refers to your Rh status.

During pregnancy, problems can occur if you are Rh negative and your fetus is Rh positive. Treatment can be given to prevent these problems.

The Rh factor is inherited, meaning it is passed from parent to child through genes. The fetus can inherit the Rh factor from the father or the mother. Most people are Rh positive, meaning they have inherited the Rh factor from either their mother or father. If a fetus does not inherit the Rh factor from either the mother or father, then the fetus is Rh negative.

When a woman is Rh negative and her fetus is Rh positive, it is called Rh incompatibility.

When the blood of an Rh-positive fetus gets into the bloodstream of an Rh-negative woman, her body will recognize that the Rh-positive blood is not hers. Her body will try to destroy it by making anti-Rh antibodies.

These antibodies can cross the placenta and attack the fetus's blood cells. This can lead to serious health problems, even death, for a fetus or a newborn.

During pregnancy, a woman and her fetus do not usually share blood. But sometimes a small amount of blood from the fetus can mix with the woman's blood. This can happen during labor and birth. It can also happen with

• amniocentesis or chorionic villus sampling (CVS)

• bleeding during pregnancy

• attempts to manually turn a fetus to be head-down for birth (move the fetus out of a breech presentation)

• trauma to the abdomen during pregnancy

Health problems usually do not occur during an Rh-negative woman’s first pregnancy with an Rh-positive fetus. This is because her body does not have a chance to develop a lot of antibodies. But if treatment is not given during the first pregnancy and the woman later gets pregnant again with an Rh-positive fetus, she can make more antibodies. More antibodies put a future fetus at risk.

Yes, an Rh-negative woman can also make antibodies after

• miscarriage
• ectopic pregnancy
• induced abortion

If an Rh-negative woman gets pregnant after one of these events and has not received treatment, a future fetus may be at risk of problems if it is Rh positive.

During a pregnancy, Rh antibodies made in a woman's body can cross the placenta and attack fetal blood cells. This can cause a serious type of anemia in the fetus in which red blood cells are destroyed faster than the body can replace them.

Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, the fetus will not get enough oxygen. In some cases, a fetus or a newborn can die from anemia. Rh incompatibility can also cause jaundice in a newborn.

Yes, problems during pregnancy caused by Rh incompatibility can be prevented. The goal of treatment is to stop an Rh-negative woman from making Rh antibodies in the first place. This is done by finding out if you are Rh negative early in pregnancy (or before pregnancy) and, if needed, giving you a medication to prevent antibodies from forming.

A simple blood test can determine your blood type and Rh status. A blood sample can be taken in the office of your obstetrician–gynecologist (ob-gyn). This sample is usually taken during the first prenatal care visit.

An antibody screen is another blood test that can show if an Rh-negative woman has made antibodies to Rh-positive blood. This test can also show how many antibodies have been made.

If you are Rh negative and there is a possibility that your fetus is Rh positive, your ob-gyn may request this test during your first trimester. You may have this test again at 28 weeks of pregnancy. In some cases, you may be tested more often.

Rh immunoglobulin (Rhlg) is a medication that stops the body from making Rh antibodies if it has not already made them. This can prevent severe fetal anemia in a future pregnancy. RhIg is given as an injection (shot).

If you are in this situation, talk with your ob-gyn about whether you need RhIg and when you might be given this medication. It is not helpful if your body has already made Rh antibodies.

A dose of RhIg is recommended in these situations:

• After a miscarriage or abortion at 12 weeks or more of pregnancy

• After an ectopic pregnancy, amniocentesis, CVS, fetal blood sampling, or fetal surgery

• If you had bleeding after 20 weeks of pregnancy

• If you had trauma to the abdomen during pregnancy

• If attempts were made to manually turn a fetus from a breech presentation

If you are less than 12 weeks pregnant at the time of miscarriage or abortion, talk with your ob-gyn about whether RhIg is right for you.

• At 28 weeks of pregnancy—A small number of Rh-negative women may be exposed to Rh-positive blood cells from the fetus in the last few months of pregnancy and may make antibodies against these cells. RhIg given at 28 weeks of pregnancy destroys these Rh-positive cells in the woman’s body. This prevents Rh-positive antibodies from being made.

• Within 72 hours after the delivery of an Rh-positive baby—The greatest chance that the blood of an Rh-positive fetus will enter the bloodstream of an Rh-negative woman happens during delivery. RhIg prevents an Rh-negative woman from making antibodies that could affect a future pregnancy. The treatment is good only for the pregnancy for which it is given. Each pregnancy and delivery of an Rh-positive baby requires a repeat dose of RhIg.

RhIg treatment does not help if an Rh-negative woman has already made antibodies. In this case, the well-being of the fetus will be checked during the pregnancy, usually with ultrasound exams.

If ultrasound exams show that the fetus has severe anemia, early delivery (before 37 weeks of pregnancy) may be needed. Another option may be to give a blood transfusion through the umbilical cord while the fetus is still in the woman's uterus.

If the anemia is mild, delivery may happen at the normal time. After delivery, the baby may need a blood transfusion to replace blood cells.

Amniocentesis [am-nee-oh-sen-TEE-suhs]: A procedure that uses a needle to take fluid and cells from the sac that holds the fetus. The fluid and cells are then tested to screen for genetic disorders and health conditions in the fetus.

Anemia: Abnormally low levels of red blood cells in the bloodstream.

Antibodies: Proteins in the blood that the body makes in reaction to foreign substances, such as bacteria and viruses.

Breech Presentation: A position where the feet or buttocks of the fetus are in place to appear first during birth.

Cells: The smallest units of a structure in the body. Cells are the building blocks for all parts of the body.

Chorionic Villus Sampling [kor-ee-AH-nik VILL-uhs] (CVS): A procedure that takes a small sample of cells from the placenta for testing.

Ectopic Pregnancy: A pregnancy in a place other than the uterus, usually in one of the fallopian tubes. An ectopic pregnancy cannot move or be moved to the uterus, so it always requires treatment.

Fetus: The stage of human development beyond 8 completed weeks after fertilization.

Genes: Segments of DNA that contains instructions for the development of a person’s physical traits and control of the processes in the body. The gene is the basic unit of heredity and can be passed from parent to child.

Induced Abortion: An intervention to end a pregnancy so that it does not result in a live birth.

Jaundice [JAWN-duhs]: A condition that causes the skin and the whites of the eyes to take on a yellow appearance after buildup of bilirubin in the blood. Bilirubin is a yellow substance that forms when red blood cells break down.

Miscarriage: Loss of a pregnancy that is in the uterus.

Obstetrician–Gynecologist (Ob-Gyn): A doctor with medical and surgical training and education in the female reproductive system.

Oxygen: An element that we breathe in to sustain life.  

Placenta [pluh-SEN-tuh]: An organ that provides nutrients to and takes waste away from the fetus.

Prenatal Care: Health care during pregnancy.

Rh Factor: A protein that can be found on the surface of red blood cells and makes up part of a person’s blood type.

Rh Immunoglobulin (RhIg): A substance given to prevent an Rh-negative person’s antibody response to Rh-positive blood cells.

Trimester: A time period of 3 months. There are three trimesters in pregnancy: the first trimester, second trimester, and third trimester.

Ultrasound Exams: Tests that use sound waves to examine inner parts of the body. During pregnancy, ultrasound can be used to check the fetus. Also called ultrasonography or sonography.

Umbilical Cord: A cord-like structure containing blood vessels. It carries oxygen and nutrients from the placenta to the fetus.

Uterus: A muscular organ in the female pelvis. During pregnancy, this organ holds and nourishes the fetus. Also called the womb.