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Rh Factor And How It Can Affect Pregnancy

During pregnancy, it is important to have a blood test to find out your blood type. More than 85% of people in the world are Rh-positive, meaning that they have the Rh antigen. This can be problematic if the mother does not have the Rh factor but the fetus’s blood does. This page will give you basic information on the Rh factor and what it can mean for your pregnancy.



Woman showing question mark on naked belly. Gentle touch. Concept of baby planning, abdomen health or girls problems. Close up. Front view

There are several different blood types, such as A type, B type, and O type. There is also an Rh factor, which is the type of protein in red blood cells. Most people have the Rh factor, meaning that they are Rh-positive. Those that do not are considered Rh negative. Whether or not you are positive does not affect your overall health. However, it can potentially affect a pregnancy.



The Rh factor causes problems when a person with Rh-negative blood comes in contact with someone with Rh-positive blood. If this occurs, the negative person will become sensitized, meaning that he or she produces antibodies to fight the Rh factor.

If an Rh-negative woman has a child with an Rh-positive man, their child can be Rh-positive. While carrying this child, the woman may become sensitized. Although the mother and fetus do not share blood systems, the fetal blood can go through the placenta into the mother’s system. This can cause a small number of Rh-negative women to react to the fetal blood as if they are allergic to it. They then become sensitized, causing antibodies to be formed that will fight and break down the fetal blood cells, producing anemia. This condition is called hemolytic disease and can be serious enough to cause illness, brain damage, or even death.

Even after the Rh-positive child is born, the antibodies do not go away. If she becomes pregnant with another Rh-positive fetus, there will be more antibodies that could cause even more serious damage. Sensitization can also occur if a mother has had a miscarriage, an induced abortion, an ectopic pregnancy, or a blood transfusion.



A simple blood test can determine if a woman is Rh-positive or negative. Another test called an antibody screen can be used to determine whether or not sensitization has occurred. Hemolytic disease in the child can be prevented if the mother has not yet developed antibodies. A medication called Rh immunoglobulin (RhIg) can help prevent sensitization by keeping her cells from being able to respond to the Rh factor. It can be injected into the arm or buttocks and is safe for pregnant women to use. The only known side effects are soreness at the injection site and slight fever, which both go away.



If an Rh-negative woman has not yet been sensitized, she may be given RhIg around the 28th week of pregnancy to prevent sensitization. If the child is Rh-positive, she should be given another dose of RhIg shortly after birth to prevent sensitization to cells left over by the fetus. No treatment is needed for an Rh-negative father. The treatment is only valid for the pregnancy for which it is given.  Rh-negative women should also receive treatment after an ectopic pregnancy, miscarriage, or induced abortion to prevent any attacks on a future fetus. RhIg may also be given after amniocentesis or postpartum sterilization.


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Rh treatments are ineffective once a woman has developed antibodies. It is important for all women to be tested during their pregnancies. In some cases of hemolytic disease, the doctor may suggest delivery at the normal time, followed by a transfusion that will replace diseased blood in the fetus. In severe cases, the fetus may be given transfusions in the womb or may need to be delivered early.



Getting a blood test is very important during your pregnancy because it can help prevent Rh sensitization. Talk to your doctor about your risk factor for developing Rh sensitization during pregnancy.