A "positive" result for a problem means that there is a higher-than-average chance your baby has that problem. If the result is "negative," or normal, it means that your baby is less likely to have the problems that are screened for in the quad screening test. But it doesn't guarantee that you will have a normal pregnancy or baby.

The accuracy of a quad screening test is based on how often the test correctly finds a birth defect.

• It correctly finds neural tube defects, such as spina bifida, in up to 80 out of 100 fetuses who have it. It finds anencephaly in about 95 out of 100 fetuses. The test misses spina bifida in at least 20 out of 100 fetuses who have it. And the test misses anencephaly in about 5 out of 100 fetuses who have it.^{footnote 1}
• It correctly finds Down syndrome in 81 out of 100 fetuses who have it. It misses Down syndrome in 19 out of 100 fetuses who have it.^{footnote 2}

Your doctor may tell you the result of your test as a set of numbers. Doctors often use a certain number as a cutoff for a positive result. For example, your doctor may say the cutoff is 1 out of 200. This means that if your result is 1 out of 200 or 1 out of a number less than 200 (such as 1 out of 100), you have a positive result and your baby has a higher chance of a birth defect. If your result is 1 out of 300, this means that you have a negative result and your baby has a lower chance of a birth defect.

With the quad test, there is a chance of getting a false-positive test result. This means that the test could be positive when the baby doesn't have the problem.

A false-positive result can cause stress and lead to tests you don't need (such as an amniocentesis). Many people who have a positive screening test result are actually carrying a healthy baby.

Sometimes negative test results can be wrong too. They may show that the baby is fine when they do have a problem. (This is a false-negative test result.)