Women of certain races or ethnic groups may be at higher risk for "hemoglobinopathies," abnormalities of hemoglobin chains that may cause a defect in the ability of the red blood cells to carry oxygen. Black women should be offered a SickleDex blood test to check for the sickle cell trait.
Platelet count is another important component. Platelets allow blood to clot, and the level should be neither too high nor too low. The count typically falls slightly in pregnancy but should never fall below 100,000. It is helpful to have a baseline evaluation, as complications in later pregnancy, such as preeclampsia, may have negative effects on clotting.
The white cell count and "differential" (separating out the types of white blood cells) is helpful if a maternal infection is suspected. On the initial visit, the white count is often slightly elevated; that's a normal finding in pregnancy. Knowing the type of the cell can help differentiate viral from bacterial infection, and the baseline count may serve as a baseline by which to compare later tests.
Blood Group (ABO) and Rh Testing
All pregnant women should have ABO and Rh typing early in each pregnancy. No one would ever receive a blood transfusion based only upon a prenatal lab report, but important information about antibodies and Rh factor is also collected. If baby is Rh-negative and mother is Rh-positive, the mother may produce antibodies against the baby's red blood cells. It's important to monitor all Rh-negative women for antibodies at the initial OB visit, at 28 weeks and after any trauma that may occur during the pregnancy.