A fetal non-stress test (NST) is a type of fetal screen performed to check on the health of a fetus after the 28th week of pregnancy. This test involves monitoring the fetal heart rate over a period of time to see if the heart rate increases when the baby moves. If it does not, it can indicate that there is a problem with the placenta or that there are other pregnancy complications. If the test shows that the fetus is “nonreactive,” meaning that there are no changes in the heart rate, this is not necessarily an immediate cause for concern. Follow-up testing is needed to learn more.
Fetal NSTs are usually recommended when women have high risk pregnancies, when a doctor is concerned about the placenta, or when a woman notices that the fetus is moving less than usual. The test is noninvasive and carries no risks. The fetal NST can be done in a clinic or doctor's office and may be performed during an appointment for a regular prenatal exam for convenience.
In a fetal NST, the woman lies on an examination table and a belt with a fetal heart monitor is placed around her belly. Every time the baby moves, the woman presses a button. The movements are matched up with readouts from the fetal heart monitor to see how the heart rate responds to movement. A “reactive” test result indicates that changes in the heart rare were observed during the fetal NST and is a good sign.
The most frequent problem encountered with a fetal NST is that the fetus is asleep or not very active. The test can be timed for a period when the fetus normally moves, and if the fetus doesn't feel like cooperating, sometimes gently touching the belly or sounding a tone will wake the fetus up and encourage it to move around. External stimuli can often evoke a response in the fetus and are usually enough to rouse the fetus for the test.
A doctor may recommend multiple fetal NST sessions over the course of a pregnancy to monitor the mother and fetus. If abnormalities are observed, ultrasound and other testing options are available to learn more about why the fetus is nonreactive. Women tend to get to know the habits of the fetus over time, and it is advisable to call the doctor if a fetus seems less active than usual to discuss possible causes and make plans for a medical appointment.