Rh Blood Type and Pregnancy

When a baby inherits a Rh+ blood type but the mother is Rh-, it is considered dangerous during pregnancy. This is because Rh+ blood types contain an identifying protein on the surface of red blood cells called Rh factor, while Rh- blood types don’t have it. If the mother were to be exposed to the Rh+ blood, which is likely during pregnancy, her immune system would react to the presence of the Rh factor she doesn’t have and make antibodies against it. These antibodies would then travel to the baby and attempt to destroy the Rh factor on the surface of its red blood cells, resulting in a series of severe health complications known as the hemolytic syndrome of the newborn.

What is Rh?
Rh refers to both the Rh blood group or Rhesus blood group and to the Rh factor specific to this blood group. The Rhesus blood group is essentially a classification of blood types according to specific cell markers on the surface of red blood cells called antigens. There are around 50 known antigens in the Rhesus blood group, all of which basically describe different blood types. By far the most important antigen is the protein called D antigen, RhD or Rh factor. The Rh factor is essentially a marker that identifies a specific structure on the surface of red blood cells.

Rh factor significance in pregnancy

The Rh factor gives two blood types in the Rh system: Rh positive blood groups (Rh+) or Rh negative blood groups (Rh-). What do the positive and the negative mean? Essentially, Rh+ blood types have the D antigen protein on the surface of red blood cells. Rh- blood types lack this D antigen protein on the surface of red blood cells. Every blood type in the ABO blood group system is either Rh+ or Rh-. This gives the following blood types: A-, A+, B-, B+, AB-, AB+, O- and O+. Both the Rh factor and ABO blood type classification are essential in order to determine blood compatibility for safe transfusions. Ideally, for every blood type compatibility in the ABO system, Rh factor must match or else there is a risk of sensitization and future incompatibility.

Rh factor and its significance. The Rh factor is used to determine compatibility of blood types for transfusions. Normally, the ABO and Rh classifications must be considered together for blood transfusions. Ideally, both the ABO and Rh blood types should match. However, it’s possible to give Rh+ blood to someone with Rh- blood and no antibodies for the Rh antigen. This can be done only once because after receiving Rh+ blood, the Rh- recipient will most likely develop antibodies for the Rh factor in the Rh+ blood. This is especially dangerous for women of child bearing age with Rh- blood because exposure to the Rh factor from Rh+ blood will result in them producing antibodies against that factor.

Rh factor and its significance in pregnancy

It’s dangerous for pregnancy when a baby inherits an Rh+ blood type from the father and the mother is Rh-. This means the baby will have the Rh factor (or D antigen), but the mother will not. If the mother and baby’s different blood types come into contact during pregnancy, which is likely, the mother’s blood will react to the Rh factor (or D antigen) in the Rh+ blood of the baby. Because her immune system does not recognize it, it will consider it a potentially harmful element and will produce antibodies against it called D antibodies.

These antibodies will look to destroy the Rh factor, but because it’s located on the surface of the red blood cells of the baby, they will essentially destroy its red blood cells which entails long term health problems. Usually, the risk is lower for a first pregnancy as the antibodies produced are generally not very able to reach the bay and produce serious complications. However, this incompatibility is especially dangerous during a second pregnancy and will result in severe complications known as the hemolytic syndrome of the newborn.

Rh factor and pregnancy

Rh factor incompatibility in pregnancy also occurs if an Rh- woman has received a blood transfusion with an Rh+ blood type sometime during her life. When an Rh- blood type is exposed to an Rh+ blood type, the immune system will get triggered and produce antibodies against the Rh factor (or D antigen) in the Rh+ blood. This is known as sensitization. If a pregnancy occurs later on and the baby is Rh+, the immune system of the mother will recognize that Rh factor in the Rh+ blood as the harmful element from the past. Antibodies will be produced against it which typically results in the destruction of the red blood cells in the baby’s blood type. A miscarriage can further cause sensitization of the Rh- mother to Rh+ blood if the baby was Rh+ and affect future pregnancies.

This cross-reaction is known as the hemolytic syndrome of the newborn and causes a series of severe complications for the baby such as:
1) Anemia due to the destruction of red blood cells or insufficient red blood cells
2) Fluid buildup, difficulty breathing
3) Enlarged spleen due to the fact that the spleen is a place where red blood cells are produced during pregnancy and stored after birth
4) Jaundice, enlarged liver due to the fact that the liver helps recycle components of red blood cells
The condition may require preterm delivery or a blood transfusion for the baby if it’s anemic.

Rh factor inheritance. Technically, a baby can inherit either an Rh positive or Rh negative blood type from parents. The only problem is when the mother is Rh- and the baby is Rh+ because then the mother’s immune system may react to the presence of the RhD antigen in the baby’s blood. This Rh factor incompatibility is screened for during pregnancy to prevent complications.
The Rh factor blood test called the indirect Coombs test (or indirect antiglobulin test) is used to screen pregnant women for possible Rh factor incompatibility by detecting antibodies against the Rh factor. If confirmed, treatment consisting of Rh-immunoglobulin is given to the mother during pregnancy to prevent complications for the baby.


What does it mean to have Rh+ blood type in pregnancy? When a mother has Rh+ blood and her baby inherits Rh- blood, complications may appear during pregnancy. If the blood types of the two come into contact, the immune system of the mother will not recognize the Rh factor in the baby blood type and will produce antibodies against it. These antibodies would then seek to destroy the red blood cells of the baby, producing serious complications. Rh factor incompatibility occurs when the mother is Rh+ and her baby inherits an Rh- blood type.

This post was updated on Friday / July 31st, 2020 at 11:37 PM