Rh/Rhesus Blood Typing

​​About Rh factor

The surface of red blood cells contains markers that the immune system can recognize. One of these markers is the Rh or Rhesus factor. A person whose blood contains the Rh factor is Rh-positive; a person whose blood does not contain the Rh factor is Rh-negative. Blood type contains information about the presence (+) or absence (–) of the Rh factor.

How people get Rh factor

Rh factor is inherited, passed to children through genes from both their mother and father. Women may carry a fetus that has a different Rh factor than their own depending on what genes the fetus inherited from the woman and her partner.

Importance of Rh factor in pregnancy

Rh factor can cause problems in pregnancy if the woman is Rh negative and carries an Rh positive fetus. This situation is called Rh incompatibility.

Rh incompatibility during a pregnancy

If an Rh negative woman’s blood is exposed to blood from an Rh positive fetus, her immune system can make antibodies to the Rh factor. These antibodies can then attack Rh positive blood cells in a Rh positive fetus in a future pregnancy. If Rh negative women develop Rh antibodies this is called Rh sensitization.

Rh sensitization in pregnancy

During pregnancy women and their fetus do not share blood systems. Small amounts of fetal blood can cross the placenta into the woman’s blood system. This can happen during pregnancy, labour and birth.

How to find out what your Rh blood type is

Blood can be tested at labs, hospitals or clinics. Common antibodies, including Rh antibodies, can also be screened for. This is routinely called a blood type and screen.

Preventing Rh sensitization

Pregnant women’s blood type is tested routinely in pregnancy. Rh negative women with no Rh antibodies are given an injection of Rh-immunoglobulin (a blood product also called Rhogam or WinRho) at 28 weeks of pregnancy or any time there is risk of being exposed to fetal blood. Woman are at risk of being exposed to fetal blood: if bleeding occurs during pregnancy, if they have an amniocentesis or chorionic villi sampling, after delivery of a Rh positive infant, or at time of miscarriage, induced abortion or ectopic pregnancy.

Risk for pregnancy complications

There is no risk. Rh positive women do not create antibodies to Rh.

 

Amniocentesis: A procedure in which a needle is used to withdraw and test a small amount of amniotic fluid and cells from the sac surrounding the fetus.

Antibodies: Proteins in the blood produced reaction to foreign substances, such as bacteria and viruses that cause infection or foreign blood proteins, like Rh.

Chorionic villus sampling (CVS): A procedure in which a small sample of cells is taken from the placenta and tested.

Ectopic pregnancy: A pregnancy in which the fertilized egg begins to grow in a place other than inside the uterus, usually in one of the fallopian tubes.

Fetus: The developing organism in the uterus from the ninth week of pregnancy until the end of pregnancy.

Genes: Segments of DNA that contain instructions for the development of a person’s physical traits and control of the processes in the body. They are the basic units of heredity and can be passed down from parent to offspring.

Induced abortion: The planned termination of a pregnancy before the fetus can survive outside the uterus.

Immune system: The system in the body that identifies and protects the body from foreign substances, cells, and tissues by producing a response to eliminate these foreign materials.

Miscarriage: Loss of a pregnancy that occurs before 20 weeks of pregnancy.

Placenta: Tissue that provides nourishment to and takes waste away from the fetus.

Rh (rhesus) factor: A protein that can be present on the surface of red blood cells.

Rh immunoglobulin (Rhogam, WinRho): A substance given to prevent an Rh-negative person’s antibody response to Rh-positive blood cells.

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