What is the Rh factor and its importance in pregnancy?

The Rh factor is a protein found on the surface of red blood cells. If your blood cells contain this protein, you are Rh-positive. If your blood cells do not contain 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 factor status [1].

The Rh factor is inherited from parents. Most people are Rh-positive. Being Rh-negative does not affect your health in general, but it can affect the fetus's health if you are pregnant [2].

The importance of Rh factor in pregnancy

The importance of the Rh factor in pregnancy arises when "Rh incompatibility" occurs. This incompatibility happens when the mother is Rh-negative and the fetus is Rh-positive [1]. In this case, the mother's body may recognize the fetus's Rh-positive red blood cells as foreign material, triggering her immune system to produce antibodies against them [2].

How are antibodies formed?

Usually, the blood of the mother and fetus does not mix directly during pregnancy. However, a small amount of fetal blood can enter the mother's bloodstream in several situations, leading to the formation of antibodies. These situations include:

• During childbirth [1]
• Miscarriage, ectopic pregnancy, or induced abortion [1]
• Medical procedures such as amniocentesis or chorionic villus sampling [1]
• Bleeding during pregnancy after the twentieth week [1]
• Abdominal trauma during pregnancy [1]
• Manual attempts to turn the fetus from a breech position [1]

These antibodies usually do not cause problems in the first pregnancy because the mother's body does not have enough time to produce a large amount of them. However, in future pregnancies with an Rh-positive fetus, more antibodies can form that may cross the placenta and attack the fetal blood cells, leading to serious health problems [1].

Potential risks of Rh incompatibility to the fetus

If antibodies are formed in the mother's body, they can attack the red blood cells of the fetus, causing a serious type of anemia. In this case, red blood cells are destroyed faster than the fetus's body can replace them. Since red blood cells carry oxygen to all parts of the body, insufficient amounts mean the fetus will not get enough oxygen. In some cases, severe anemia may lead to fetal or neonatal death. Rh incompatibility can also cause jaundice (yellowing) in newborns [1].

Prevention and next steps

Rh incompatibility problems in pregnancy can be prevented. The goal is to prevent the Rh-negative mother's body from forming antibodies in the first place [1]. This is done through:

• Blood type and Rh factor test: A simple blood test is performed to determine your blood type and Rh factor status, usually during the first prenatal care visit [1].
• Antibody screening: If you are Rh-negative, your doctor may order an antibody test to see if your body has already produced them. This test may be performed in the first trimester of pregnancy and again at 28 weeks of pregnancy [1].
• Rh immune globulin (RhoGAM) injection: This medication prevents the body from forming Rh antibodies if it has not already produced them. This injection is given in specific situations, such as at 28 weeks of pregnancy, within 72 hours after the birth of an Rh-positive baby, or after a miscarriage, ectopic pregnancy, or certain medical procedures [1]. It is important to discuss the timing and dosage of the RhoGAM injection with your doctor [1].

If you are diagnosed with Rh incompatibility, your doctor will monitor your condition and that of the fetus closely. For more information on managing Rh factor incompatibility in pregnancy, you can visit Management of Rh factor incompatibility in pregnancy: Your guide to the preventive injection and preventive measures (Arabic).

Medical references

• The Rh Factor: How It Can Affect Your Pregnancy
• Rh Incompatibility
• Fetal-maternal erythrocyte distribution blood test