Blood Types in Pregnancy

Every person has a blood type, (O, A, B, or AB) and an Rh factor, either positive or negative. The blood type and the Rh factor simply mean that a person's blood has certain specific characteristics. The blood type is found as proteins on red blood cells and in body fluids. The Rh factor is a protein that is found on the covering of the red blood cells. If the Rh factor protein is present on the cells, the person is Rh-positive. If there is no Rh factor protein, the person is Rh- negative.

The following are the possible combinations of blood types with the Rh factors:

Rh Positive Blood Types:
A+, B+, 0+ and AB+

Rh Negative Blood Types:
A-, B-, 0- and AB-

Rh factors are genetically determined. A baby may have the blood type and Rh factor of either parent, or a combination of both parents. Rh factors follow a common pattern of genetic inheritance. The Rh-positive gene is dominant (stronger) and even when paired with an Rh-negative gene, the positive gene takes over.

• If a person has the genes + +, the Rh factor in the blood will be positive.

• If a person has the genes + -, the Rh factor will also be positive.

• If a person has the genes - -, the Rh factor will be negative.

A baby receives one gene from the father and one from the mother. More specifically, consider the following:

If a father's Rh factor genes are + +, and the mother's are + +, the baby will have one + from the father and one + gene from the mother. The baby will be:

• + + Rh positive

If a father's Rh factor genes are + +, and the mother's are - -, the baby will have one + from the father and one - gene from the mother. The baby will be:

• + - Rh positive

If the father's genes are + - Rh positive, and the mother's are + - Rh positive, the baby can be:

• + + Rh positive
• + - Rh positive
• - - Rh negative

If the father's genes are - -, and the mother's are + -, the baby can be:

• + - Rh positive
• - - Rh negative

If the father's genes are - -, and the mother's are - -, the baby will be:

• - - Rh negative

Problems with the Rh factor occur when the mother's Rh factor is negative and the baby's is positive. Sometimes, an incompatibility may occur when the mother is blood type O and the baby is either A or B.