The nonstress test (NST) measures the fetal heart rate (FHR) as the fetus moves. When the fetus is moving around, its heart typically beats faster. During the NST, a belt with transducers is placed around the pregnant woman's waist for 20-30 minutes. Doppler ultrasound is used to measure the fetus' heart rate patterns, and a record is made on graph paper. When the fetus is asleep or resting, it may not move for a short period of time—sometimes as long as 40 minutes. The healthcare provider may try to wake the fetus by having you eat or drink something, or by using sound.
Your healthcare provider may recommend this test during the third trimester, as well as other tests, if you have a medical condition that could put you at risk for having problems with your pregnancy. Examples of conditions that could put you or the baby at risk include:
You may also have this test if:
The NST is not always accurate. Sometimes the test suggests a problem even when the fetus is healthy (a so-called false-positive result). If there is no change in fetal heart rate in response to fetal movement, your healthcare provider may want to try another test to confirm the NST test results. Your healthcare provider may suggest other tests so that she can gather important information about the health of your fetus. A problematic test result (eg, no increase in FHR with fetal movement) often suggests that you need special care. It does not necessarily mean that your fetus is in trouble. Your healthcare provider will be able to answer questions and discuss any concerns you have about monitoring.