NST Machine

A non-stress test (NST) machine is used to detect changes in your unborn baby's heartbeat. Electrodes like those used with an electrocardiogram are placed on your abdomen. The baby's heartbeat can be monitored on a computer screen and/or recorded on a strip of paper. They will also show if you are having uterine contractions and how long these last. If you are having contractions, the test is invalid because the baby is under stress from these. 

Testing
Your doctor wants to know if your unborn baby's heart rate goes up when it moves around in utero, to see if it is ready to withstand the stress of labor. During the test you will sit leaning back against a support with your knees up and a cushion under one hip. You may be given a button to push when you feel your baby move; this will put a mark on the paper in addition to the tester's notes, since you may feel movement before it is seen. 

Getting the Baby to Move
If the baby is sleeping, it may not move for a while. To get it to move for the test, you may be asked to eat or drink something or put your hands on your belly and physically move the baby around gently. The tester may even try sending sounds through your abdominal wall to encourage your baby to move. 

Results
A normal heart rate for a resting fetus is 120 to 160 beats per minute, and this should go up by at least 15 beats when the baby moves. This is called a "reactive" test. For a valid test, this should happen at least twice within 20 minutes. The test is "non-reactive" if the heartbeat does not increase with movement.