In most cases, when picking out a donor, the blood type of the donor is of little or no consequence, as long as your OB doctor is made aware of it. The blood type of the donor is important only when trying to make sure that the childs blood type would be compatible for the parents involved, or if there is some type of blood problem.

Every person has TWO genes that determine blood type. When a lab checks your blood type, the result does not always reflect BOTH of the genes because the "O" variant of the gene is "silent". Because of this the "O" is expressed in the blood type only when both genes are type "O". Human blood is classified, or typed, according to the presence or absence of certain markers (called antigens) on the surface of red blood cells.

In the table below, the first column shows all the possible combinations of the two blood type genes. The second column shows what the laboratory would report for the person's blood type. Notice that an O gene makes no contribution to the blood type.

• AA genes -- lab says "type A"
• AB genes -- lab says "type AB"
• AO genes -- lab says "type A"
• BA genes -- lab says "type AB"
• BB genes -- lab says "type B"
• BO genes -- lab says "type B"
• OA genes -- lab says "type A"
• OB genes -- lab says "type B"
• OO genes -- lab says "type O"

Example 1

Here is one possibility that lets a type B parent have a type A child. Suppose Mom's genes are AB (across the top) and Dad's genes are BO(down the left side). The lab says Dad has type B blood. Suppose baby inherits Mom's A gene and Dad's O gene. This gives baby an AO gene pattern, which the lab measures as type A blood. There are four different genetic combinations possible for the child from these two parents, but only three different blood types as shown in the table below. The three types would be types AB, A, or B.

Example 2

Example 3

The ABO test classifies people's blood into one of four types: A, B, AB, or O.

If your red blood cells have:

• The A antigen on their surface, you have type A blood. The liquid portion of your blood (plasma) contains antibodies against type B blood.
• The B antigen on their surface, you have type B blood. Your plasma contains antibodies against type A blood.
• Both the A and B antigens on their surface, you have type AB blood. Your plasma does not contain antibodies against either type A or type B blood.
• Neither the A nor B antigen, you have type O blood. Your plasma contains antibodies to both A and B.

Type O negative blood does not have any antigens. It is called the "universal donor" type because it is compatible with any blood type. Type AB positive blood is called the "universal recipient" type because a person who has it can receive blood of any type. Although "universal donor" and "universal recipient" types are occasionally used to classify blood in an emergency, blood typing tests are almost always done to prevent transfusion reactions.

Rh test

Rh blood typing determines the presence (+) or absence (-) of the Rh antigen (also called the Rh factor). If your red blood cells: ·

• Contain the Rh antigen, your blood is Rh positive. ·
• Do not contain the Rh antigen, your blood is Rh negative. ·
• Contain the A and Rh antigens, your blood type is A positive (A+).
• If your blood contains the B antigen but not the Rh antigen, your blood type is B negative (B-).

Pregnancy

Always make sure to get good professional OB care. You will need to make your physician aware of your pregnancy and the blood type of the biological father. We list the blood types of all donors in the donor listing for this purpose. If your doctor is made aware of this information, almost all problems that could be encountered from blood types can be taken care of and avoided. Rh blood typing is especially important for pregnant women. A potential problem arises when a woman who has Rh negative blood becomes pregnant with a fetus that has Rh positive blood. This is called Rh incompatibility. If the blood of an Rh positive fetus mixes with the blood of an Rh negative woman during pregnancy or delivery, the mother's immune system produces antibodies. This antibody response is called Rh sensitization and, depending on when it occurs, can destroy the fetus's red blood cells. Rh sensitization does not usually affect the health of the fetus during the pregnancy in which the sensitization occurs. However, the fetus of a subsequent pregnancy is more likely to be affected if the fetus's blood type is Rh-positive. Once sensitization has occurred, the fetus can develop mild to severe problems (called Rh disease, hemolytic disease of the newborn, or erythroblastosis fetalis). If untreated, complications from sensitization can, in rare cases, lead to the death of an Rh positive fetus. Rh testing is done in early pregnancy to detect a woman's blood type. If she is Rh negative, she can receive a vaccine called Rh immune globulin (such as RhoGAM) that almost always prevents sensitization from occurring. Problems arising from Rh sensitization have become very rare since the Rh immune globulin vaccine was developed. Always get good OB care!