False Positives: Why They're Not Always a Bad Thing

By Kristen J. Gough

False Positives: Why They're Not Always a Bad Thing

In this article:
Understanding Tests—Diagnostic vs. Screening
The Triple Screen
New Screening Tests
Amniocentesis and Chorionic Villus Sampling (CVS)
Why Tests Are Important
Refusing Tests
Working with Your Healthcare Provider

A positive prenatal test result doesn't always mean there's something wrong with your baby. In fact, false positives are more common than you think.

During pregnancy, you're poked and prodded to provide blood, urine, and ultrasound images, all in hopes of finding definitive answers about your body and your baby. Yet many tests you'll experience during pregnancy aren't yes or no tests—they can't necessarily determine that you'll have a healthy baby or that something isn't right. Instead, many prenatal tests are looking for whether your baby is at a greater risk of having certain problems based on the results. Learning more about prenatal testing can relieve anxiety, especially if you are one of the many women who get a false positive.

Understanding Tests—Diagnostic vs. Screening

"The most important preliminary point to understand with all prenatal tests is the difference between a screening test and a diagnostic test," explains Erica Lyon, author of The Big Book of Birth and the founder and director of Realbirth, a childbirth education center in New York City. "A screening test shows perhaps a possible increased chance of something existing whereas a diagnostic test determines if something does, in fact, exist."

The Triple Screen

The triple screen is perhaps one of the most misunderstood of the prenatal tests. The triple screen (also known by several other names including the multiple marker screening and maternal serum screening) is a blood test administered at 15 to 20 weeks. It looks at the levels of three pregnancy hormones—hCG (human chorionic gonadotrophin], estriol, and AFP (alpha-fetoprotein)—in your bloodstream; elevated levels of these hormones may indicate a problem.

"The triple screen is a screening test," says Lyon. "The most important thing to understand specifically about the triple screen is that it has an inordinately high false-positive rate, meaning it often shows an increased chance, when in fact, absolutely everything is all right."