Significance of Rare Blood Types

Human blood types are classified using two primary systems:

ABO SYSTEM:

This system categorizes blood based on the presence of Antigen A and Antigen B on red blood cells, with the following distribution:

Blood type A: about 24%
Blood type B: about 34%
Blood type O: about 38% (the most common)
Blood type AB: about 8% (the least common)

Rh SYSTEM:

This classification is based on the presence of Antigen D on red blood cells, divided into:

Rh-Positive: Individuals with Antigen D present on their red blood cells (commonly found).
Rh-Negative: Individuals lacking Antigen D, which occurs in only about 15% of white individuals and is very rare in Thailand, affecting just 3 out of 1,000 people. This group is considered to have “rare blood types” or “special blood types.”

Importance of Rare Blood Types

In medical situations that require blood transfusions, individuals with Rh-Negative blood must receive Rh-Negative blood to avoid stimulating the immune system to produce antibodies that attack Antigen D on red blood cells.

In emergencies, an Rh-Negative individual can receive Rh-Positive blood only once. If they receive it again, their immune system may generate antibodies that destroy any red blood cells containing Antigen D.

Antigen D and Associated Risks

Precautions for Mothers with Rh-Negative Blood Type

If a mother has Rh-Negative blood and the father has Rh-Positive blood, the following precautions should be considered:

In the first pregnancy, if the baby has Rh-Positive blood like the father, there is a high risk that the baby’s red blood cells will enter the mother’s bloodstream during placental separation. This will prompt the mother’s immune system to produce Antibody D against the Antigen D on the baby’s red blood cells. The first child in this pregnancy will be safe.
In the second pregnancy, if the baby is Rh-Negative like the mother, the baby will be safe. However, if the baby is Rh-Positive like the father, a dangerous situation can arise because the mother has already produced Antibody D from the first pregnancy. This antibody can attack the red blood cells of the second child, potentially leading to jaundice and, in severe cases, death.

“Therefore, women with Rh-Negative blood should consult a doctor to plan ahead for pregnancy and take preventive measures to avoid harm to the fetus.”