Nonstress Test

What a nonstress test in pregnancy can reveal

One of the most prevalent prenatal tests in late pregnancy, the nonstress test (or NST) is prized for its accuracy and, as its name implies, the fact that it does not stress the fetus at all. This is the test your doctor will order if there's any reason to believe that your little one might not be moving as frequently as usual, if you have any condition that puts your pregnancy at risk or if you've passed your due date and there's a chance your baby may not be thriving in your womb anymore.


It's never easy to sit through a major prenatal evaluation, but take comfort in the fact that this test will clearly indicate how your baby is faring. In fact, many women have the nonstress test to thank for their healthy delivery and their newborn's wellbeing. Once you understand what the test is about, how it's performed and what it will ultimately do for you and your baby, you're bound to feel more at ease when you visit your doctor for the procedure.

The NST Test Procedure

The process is quite similar to a regular labor setup: you'll be hooked up to a fetal monitor, with one belt around your abdomen to measure fetal heart rate and another to measure your contractions. The object of the test is to measure your baby's heart rate in relation to his muscle movements, since a healthy heart will react to more body movement. The test will typically last about 30 minutes, but since your doctor or radiologist will need to compare how the heart behaves when your baby is resting and how it behaves when he's active, you may need to wait for him to wake up if he's particularly drowsy.

Since your baby must have developed enough to respond to the procedure, a nonstress test will only be conducted after 28 weeks. After this point, it's easier to measure the changes in heartbeat alongside the changes in fetal movement, and an abnormally slow heart rate could indicate that the baby isn't getting enough oxygen. In turn, lack of movement, slow heart rate or other abnormal movements may lead your doctor to suspect a problem with the umbilical cord or placenta.

What the Fetal Heartbeat Monitor will Tell You

The results of the fetal nonstress test can be characterized as either reactive or nonreactive. A reactive result means that there were two or more heart rate accelerations in a 20 minute period, which shows that enough blood flow and oxygen is getting to the fetus. On the other hand, a nonreactive result indicates less than two accelerations over the same amount of time, and further tests and more fetal monitoring will be conducted to get to the bottom of the problem.

But while fetal monitors are undeniably helpful, they can also be misleading. In the case of the nonstress test, poor positioning of the baby or a doctor's misinterpretation can lead you to believe that your baby is in trouble when he is actually stable and healthy. If your baby has received a nonreactive score, stay positive and listen to the medical advice that your doctor or radiologist offers -- there are other tests that can refine those first observations, and there's also a good chance that your baby will do better if labor is induced so you can deliver him early.