RH Factor In Blood

What is Rh Factor

In 1940, Austrian-American physician Karl Landsteiner discovered an antigen (a substance that triggers the production of antibodies to kill or neutralize foreign invaders, such as bacteria and viruses) on the surface of red blood cells. This antigen was named Rh Factor, short for “Rhesus Factor”, and was named after the Rhesus monkeys that were used by Karl Landsteiner for his study.

Not all people have Rh Factor. Those who have Rh Factor are Rh-positive, while Rh-negative denotes the absence of Rh Factor in the blood. Those who are Rh-positive have no problem receiving blood from people who are Rh-negative. However, Rh-negative people cannot receive blood from Rh-positive people.

If an Rh-negative person receives blood from an Rh-positive person, the Rh-negative person will develop antibodies that will fight the Rh Factor as if it were a harmful substance. As a result of this, the red blood cells of the donated blood (which is Rh-positive) will get broken down, and this, in turn, can have fatal consequences. Rh Factor, however, has no bearing on a person’s overall health.

The characteristic of Rh-negative blood to form antibodies against Rh Factor when it comes into contact with Rh-positive blood can cause serious complications during pregnancy.

Rh Factor and pregnancy

Before we discuss how Rh Factor can cause problems during pregnancy, it is necessary to understand that children get their Rh Factor from either of their parents. For instance, if both the parents are Rh-positive, then the child too will be Rh-positive. In case one parent is Rh-positive and the other one is Rh-negative, then the child can be either Rh-positive or Rh-negative. However, the Rh Factor of the child is only known after birth.

The Rh Factor does not matter during a pregnancy when the mother is Rh-positive. The problem occurs only when the mother is Rh-negative. Such a scenario can lead to Rh incompatibility; a condition in which the mother’s Rh-negative red blood cells develop antibodies against the Rh-positive fetal cells and destroy the baby’s circulating blood cells.

What is Rh incompatibility?

As mentioned above, Rh incompatibility is a condition in which the mother’s blood cells create antibodies to fight Rh-positive fetal cells. This happens because the Rh Factor present in fetal cells is perceived by the mother’s immune system as harmful.

While it is true that the mother and the fetus do not share the blood systems, some blood cells from the fetus can cross the placenta and enter the mother’s bloodstream. If the mother is Rh-negative, her immune system perceives the Rh-positive fetal cells as being dangerous and makes antibodies that attack the blood of the Rh-positive fetus. The attack from the antibodies causes fetal red blood cells to break down. This in turn causes anemia, which can develop into a serious illness or even cause the death of the fetus or newborn.

Rh incompatibility can have dire consequences, but the good news is that the condition is completely preventable.

First Pregnancy

The Rh Factor test is one of the first prenatal tests doctors recommend. This test is very simple and does not require any special preparations.

If the mother is found to be Rh-negative, then the doctor recommends an antibody screening test (a test done to detect antibodies to Rh-positive red blood cells) during the first trimester and the 28th week of the pregnancy.

In most cases, Rh incompatibility is not an issue during the first pregnancy as the mother’s immune system takes time to develop antibodies (Rh antibodies) against the Rh-positive fetal blood cells. However, a small number of women can start producing antibodies against the Rh-positive fetal red blood cells during the last 3 months of pregnancy. That is why your doctor may recommend an injection of Rh immunoglobulin (Rhlg), a blood product that prevents the immune system of Rh-negative women from responding to Rh-positive fetal red blood cells around the 28th week of pregnancy.

If your child is Rh-negative, you don’t require a repeat dose of Rhlg. However, if the child is Rh-positive, your doctor will give you another dose of Rhlg.

You need to remember that the Rhlg treatment is good only during pregnancy. Should you get pregnant again, the chain of events will need to be repeated, that is, you will be given the Rhlg injection during and after pregnancy if your child is Rh-positive.

Other conditions when Rhlg is given

Rhlg dose is given to an Rh-negative mother after every situation in which the mother’s Rh-negative blood could is exposed to Rh-positive red blood cells, including:

  • Abortion
  • Miscarriage
  • Molar pregnancy
  • Ectopic pregnancy
  • Bleeding during pregnancy
  • Blood transfusion
  • Amniocentesis
  • Chronic villus sampling

What if the mother’s immune system has already started making Rh antibodies?

This is not a desirable situation, and regular checkups during pregnancy will be required to see if the fetus is at risk. Please note that Rh immunoglobulin treatment does not work if Rh antibodies are already present in the mother’s blood.

In more severe cases, a baby with anemia may be prematurely delivered or be given blood transfusions while still in the uterus. In less severe cases, the baby may be delivered at the normal time and may require a blood transfusion after delivery.

Rh incompatibility can cause serious complications during pregnancy. The good news is that the condition is completely preventable. Take good prenatal care if you are pregnant to ensure your baby is unaffected in case you are Rh-negative and if the baby is Rh-positive.



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