Over the course of your pregnancy, many tests will be offered or recommended. Sometimes the number of tests and tubes of blood make my patients feel like we are vampires sucking them dry. Amidst this number of tests, it's still important that you understand what tests are being done and, together with your providers, choose just those that are right for you.
Many tests are designed to optimize a mother's health not only because we want all women to be as healthy as possible, but also because a healthy mother is best for a healthy pregnancy and child. Because there is little controversy about these desired outcomes, many of these tests are done routinely and patients may not know all that is being sent or checked.
Some tests check for infection (e.g. urinary tract infections). While treating infections can be important, the nature of some infections, such as HIV, are such that patients should be informed about the test and given the option to decline having it (so called "opt out" testing, which is endorsed by many professional groups, including the Centers for Disease Control).
Other tests look for anemia (low red blood cell counts) that can be treated with iron or other vitamins. A mother's blood type is also checked to see if she is RH negative or has developed antibodies that could, rarely, indicate an incompatibility with her baby's blood type. Such incompatibilities can lead to anemia in the developing fetus and may require special testing or, very uncommonly, a blood transfusion given while the baby is still unborn (intrauterine transfusion). Women who are Rh negative and having babies fathered by Rh positive men require treatment to prevent developing antibodies that can cause the problems of isoimmunization.
During pregnancy women are also offered---but may choose not to pursue---testing to evaluate their chances of having a pregnancy affected with certain genetic conditions. The tests offered may depend on a patient's background (ethnic group, country of origin), family history (diseases or other conditions in parents or siblings) or past pregnancy history (a prior child with a disease or condition). Ashkenazi women and men (individuals with an Eastern European Jewish background) are offered screening for Tay Sachs disease, for example. African Americans may be screened for sickle cell anemia. A woman whose sister had a child with hemophilia (poor clotting of blood) may be offered screening to see if, like her sister, she is a carrier and therefore at risk for having an effected son (this disease only affects males, though females can carry the gene.
All patients should also be offered a combination of blood and ultrasound tests to help evaluate their risk of carrying a fetus with genetic conditions caused by carrying an extra chromosome. Most of us have 46 chromosomes--23 inherited from our mother, 23 from our father. Rarely, individuals will have 47 chromosomes: the most common such condition is trisomy 21--an extra number 21 chromosome, also known as Down syndrome. The chances of having a child with Down syndrome usually isn't an inherited risk (meaning that whether or not you or your family have had pregnancies with this conditions doesn't change the chance that a certain pregnancy will be effected). Down syndrome risk increases with the age of the mother (well actually, the age of the egg involved in conception, which can be quite different from a mother's age if a donor egg was used in the process of in vitro fertilization).
Women who are identified as carriers of a fetus with mutations in individual genes or as being at increased risk based on screening tests for Down syndrome or other similar conditions may elect diagnostic testing to directly examine fetal genetic material. Amniocentesis is one such diagnostic test. Some may want such testing in order to prepare for the birth of a child with medical or other needs. Others may use the information from these tests to make decisions about continuing their pregnancy.
For many, however such testing is not of interest: They don't want to know about possible conditions in their child in advance of birth. The miscarriage risk from diagnostic testing, even if it is less than 1%, seems too high. They'd never consider an abortion.
Saying that all women should be offered certain tests is not the same as saying that all women should have them. I want to emphasize that point because, almost certainly, someone will read what I've written and write an angry response that I'm recommending that all patients be screened for Down syndrome, cystic fibrosis, or some other condition that they feel does not merit anyone's considering pregnancy termination. That is not what I'm saying, and not what I do. I offer appropriate screening to all my patients, help them understand what information the test might provide and how the results might be used, and happily except their decision, whatever it might be.
Yes, there are a lot of tests in pregnancy but that doesn't mean you should be in the dark. Ask what you're being testing for and why a test is offered or recommended. Understand what the results might mean. Decide if any or all tests are right for you.