A nonstress test is used in pregnant women to evaluate the heart rate of an developing baby (fetus). Normally, a developing baby's heart rate ranges from 100 to 160 beats per minute, and it usually speeds up after the baby moves. If the heart rate is faster or slower than this range or does not speed up after the baby moves, it may mean that the baby is not doing well.

During the test:

• Elastic belts with two sensors are placed on the woman's belly. The sensors are connected to an electronic monitoring machine.
  • One sensor monitors the baby's heart rate.
  • The other sensor is a pressure gauge, which measures the strength and length of tightening (contractions) of the woman's uterus if they occur.
• The woman pushes a button on the machine every time she feels the baby move.
• The baby's heart rate is compared during movement and during contractions. Normally, the baby's heart rate increases when the baby moves. But the heart rate may not increase during the testing period.

A nonstress test usually takes about 30 minutes. It can be done in a hospital or the doctor's office.