During pregnancy, women routinely have various prenatal tests to monitor their baby’s health and development and screen for potential problems. A nonstress test (NST) is a type of prenatal test commonly done to check the baby’s heart function and oxygen supply.

Also known as fetal heart rate monitoring, the NST monitors the baby’s heart rate to test how it responds to the baby’s movements.

It’s called a “nonstress” test because no stress is placed on the developing baby during the test – their heart rate and movements are simply monitored. The NST is usually performed during the later stages of pregnancy, most commonly after 32-36 weeks.

Who Needs a Nonstress Test?

Not all pregnant women have nonstress tests. They are generally recommended when:

  • There is more than one baby
  • The mother has an underlying medical condition such as diabetes or high blood pressure
  • The mother is two weeks or more past her due date
  • There is a history of complications in previous pregnancies
  • The baby has decreased fetal movements or possible fetal growth problems
  • There is a concern with the baby’s Rh factor (hemolytic disease of the newborn)
  • The amniotic fluid is low

What to Expect from a Nonstress Test

Nonstress tests might be performed in your doctor’s office or in a perinatal center. You will recline in a chair, and your blood pressure will be checked before the test.

You’ll also have monitors attached to two belts placed across your abdomen. One monitor records your baby’s heart rate, while the other records your uterine contractions. During the nonstress test, the doctor is monitoring increases in your baby's heart rate, which should occur with fetal movements, and is a signal that your baby is receiving enough oxygen.

The test usually lasts about 20 minutes, but may take longer if your baby is asleep or not active.

Nonstress Test Results

Nonstress test results are categorized as reactive or nonreactive:

  • The result is considered reactive, or normal, if your baby’s heart rate increases to a certain level during activity. These levels may vary depending on how far along you are in your pregnancy.
  • The result is nonreactive if your baby’s heart rate does not increase to the expected level. This could happen if your baby was asleep or not active. If the NST is nonreactive, an additional test such as a biophysical profile may be done to assure you baby is healthy.

After the test, we'll discuss your results with you and let you know if additional testing or care is needed. Some women have frequent nonstress tests throughout their pregnancy to monitor the baby’s heart function and oxygen level until delivery.

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