There are certain basic blood tests one needs prior to getting pregnant or early in pregnancy. All women should have a complete blood count to check for anemia, a type and screen to check your blood type and see if you have any antibodies that could affect the fetus' blood count, a Rubella titer to see if you are immune to German measles (if you contract Rubella during pregnancy, the fetus can be severely affected), an HIV test, and a test for the Hepatitis B antigen.
Other blood tests are determined by your history. For example, if you have a personal or family history of thyroid disease, then thyroid function tests should be sent. Depending on your ethnic background, your doctor may screen you and/or your partner to see if you carry a gene for certain inherited diseases, such as Cystic Fibrosis and Tay Sachs.