An Introduction To Blood Type And Rh System Testing And Why Obstetricians Must Perform These Tests

Early on in a mother's pregnancy, her obstetrician will perform a variety of blood tests. Two things that the obstetrician will determine during these tests are the mother's blood type and whether her blood is positive or negative. 

Blood Type And Rh System Type

During the first visit, the obstetrician will likely determine the patient's blood type based on the ABO blood type system and Rh system. The ABO blood type test will reveal whether the mother has type A, type B, type AB, or type O blood. The Rh system test will further identify the mother's blood type as positive or negative, which is determined by whether Rh antigens are present or absent on her red blood cells. If the Rh antigens are present, the blood type is positive; if the antigens are absent, then the blood type is negative.

Determining the blood type and whether it is positive or negative is important in case the mother needs a blood transfusion, in case complications need to be prevented or in case the mother and fetus do not have compatible Rh systems. 

Possibility Of A Blood Transfusion

A pregnant mother might need a blood transfusion for one of two reasons: anemia or hemorrhaging

  • Anemia occurs when either the mother's blood lacks a substantial amount of an iron-rich protein called hemoglobin or her red blood cell count is significantly lower than it should be. Over the course of the pregnancy, the mother's obstetrician will monitor her red blood cell and hemoglobin counts as a proactive measure.
  • Hemorrhaging occurs when the mother loses too much blood, either during the pregnancy or following the baby's birth. This is an emergency situation requiring an immediate transfusion. Because a mother's need for a blood transfusion is often immediate, the obstetrician will need to know her blood type and whether it is positive or negative beforehand; transfusion of the wrong blood can lead to severe complications and even death.

Mother-Fetus Rh Incompatibility

Just because a mother's blood has Rh antigens does not mean that the fetus will also have Rh antigens; on the same token, a fetus can still have Rh antigens even if the mother does not. A situation in which the father has a positive blood type and the mother has a negative blood type can give rise to a condition known as "mother-fetus Rh incompatibility." This occurs when the mother's blood develops antibodies against the Rh antigens present on the fetus's red blood cells. These antibodies will not likely cause a problem during the mother's first pregnancy but could endanger the fetus in the mother's second pregnancy. By knowing the mother's Rh type early on in the pregnancy, the obstetrician can place her on a preventative injection regimen that will limit the mother's development of Rh antigen antibodies.

For more information, contact a business such as Women's Care Inc.