To Test or Not to Test?

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Screening tests versus diagnostic tests . The pros and cons of prenatal testing . Why the age argument doesn't hold water . Alpha-fetoprotein (AFP) . The different types of prenatal tests . What to do if the test brings bad news

To Test or Not to Test?

To our mothers' and grandmothers' generations, modern prenatal tests must sound like the stuff of which science fiction novels are made. Miniature cameras inserted right into the uterus allow doctors to assess the well-being of the developing baby. Samples of amniotic fluid, umbilical cord blood, and fetal tissue provide expectant parents with a genetic and chromosomal fingerprint of their unborn child. And a simple blood test can be used to predict the probability that a particular woman will give birth to a child with either a neural tube defect or Down syndrome.

Although prenatal tests have proven beneficial to large numbers of pregnant women, the information they provide doesn't come without a price. Prenatal tests can cause unnecessary stress to couples who might otherwise be enjoying problem-free pregnancies and, in a small percentage of cases, can lead to complications that may result in the loss of an otherwise healthy baby.

In this chapter, we provide you with the facts you need in order to make informed choices about prenatal testing. We discuss the pros and cons of prenatal testing, the risks and benefits of the various types of tests, and the options you have in the event that the test brings bad news rather than good.

" I didn't have any genetic testing done since there is no family history of disease and I didn't think I could handle the stress of waiting for the results.
—Laura, 21, pregnant with her first child "

Tests, tests, and more tests
Prenatal tests fall into one of two basic categories: screening tests and diagnostic tests.

Prenatal screening tests are designed to do what their name implies—to screen a large number of women in order to identify those who have a higher-than-average risk of giving birth to a child with a serious or life-threatening health problem (in the case of the alpha-fetoprotein, or AFP, test) or of developing gestational diabetes (in the case of the glucose tolerance test—a test we'll discuss in Chapter 15). Screening tests are not designed to say definitively that there is a problem. Their job is simply to alert a pregnant woman and her caregiver to the possibility that there could be a problem.

Diagnostic tests, on the other hand, pick up where screening tests leave off. They are used to determine whether there is, in fact, a problem. Diagnostic tests that are commonly used in pregnancy include amniocentesis, chorionic villus sampling, level 2 or targeted ultrasound, and the three-hour glucose tolerance test.