Certain lab tests are part of routine care during pregnancy. Some of these tests are done with a blood sample. Others use a urine sample or a sample of tissue taken from your vagina, cervix or rectum. These tests can help find conditions that may increase the risk of complications for you and your fetus. Many problems found by these tests can be treated during pregnancy. Diagnostic tests can detect many, but not all, birth defects caused by defects in a gene or chromosome. Diagnostic testing may be done instead of screening if a couple has a family history of a birth defect, belongs to a certain ethnic group, or already has a child with a birth defect. Diagnostic tests also are available as a first choice for all pregnant women, including those who do not have risk factors. Some diagnostic tests carry risks, including a small risk of pregnancy loss.