What is a nonstress test (NST)?

A nonstress test  (NST) serves as a screening measure for assessing fetal health by gauging the fetal heart rate and its reaction to movement, confirming sufficient oxygen supply. This safe and painless procedure imposes no stress on the mother or the fetus. If the fetal heart rate does not respond to the movement or there is no fetal movement, the doctor may recommend additional tests to explore the possibility of oxygen insufficiency.

Why do you need a nonstress test during pregnancy?

A nonstress test is usually ordered in the following instances:

• Your pregnancy is overdue or surpasses 40 weeks, which can lead to complications.
• Your pregnancy is high-risk due to diabetes or hypertension, requiring close monitoring of you and the fetus. 
• You have multiple pregnancies.
• You have Rh-negative blood and the fetus is Rh-positive. This can lead to serious complications because your body may make antibodies against the fetal blood.
• The fetal movement decreases.
• The fetus is small for gestational age.
• You have a history of fetal death.

When is a nonstress test conducted?

It is typically performed after 28 weeks of pregnancy as the fetal heart rate begins to respond to movements.

What are the procedures of a nonstress test?

Before the procedure, you should empty your bladder. You will lie supine on an examination table. Two elastic belts with built-in sensors will be securely wrapped around your abdomen to monitor contractions and record the fetal heart rate. If the fetus appears inactive during the test, it might be in a sleep state. Your doctor may use a small noisemaker on your abdomen to gently wake the fetus. In certain instances, taking a snack or sugary beverage beforehand may stimulate fetal activity during a nonstress test. The entire procedure typically lasts about 30 minutes. Following the test, your doctor will analyze the recorded data. And discuss and explain the results with you.

What are the results of a nonstress test?

The result can be reactive or nonreactive.

• Reactive NST: The fetal heart rate accelerates in response to movement or contractions with at least two accelerations occurring within a 20-minute testing period.
• Nonreactive NST: The fetal heart rate doesn't increase with movement or there is no movement at all. Potential reasons range from insufficient oxygen supply to the possibility that the fetus was exceptionally sleepy. Certain medications can contribute to nonreactive results.

You may need additional tests including:

• Biophysical profile: Combining a nonstress test with an ultrasound.
• Contraction stress test: Assessing the fetus's reaction to contractions induced by medication, simulating labor contractions without initiating labor.
  If the test results suggest a risk of complications for the fetus, closer monitoring or early delivery may be recommended.

FAQ

• What should I do if the fetus does not move during a nonstress test?
  You do not have to worry if the fetus is not moving. Your doctor may use a buzzer or provide a sugary drink or snack to wake up the fetus and stimulate movement.
• What does it mean to fail a nonstress test?
  A nonreactive result does not imply fetal distress but may necessitate further testing to explore the reason for the nonreactive result.
• Can a nonstress test determine the fetus's sex?
  No, a nonstress test is not designed to determine the fetus's sex.
• Is a nonstress test similar to a stress test?
  • A nonstress test should not be confused with an exercise stress test. The former assesses the fetal heart rate to monitor changes during movement or uterine contractions, and you will be in a reclined position during the test.
  • A stress test assesses your heart rate, blood pressure, and oxygen levels under stress, usually during activities like walking on a treadmill or pedaling a stationary bike with chest monitors. This test aids your provider in understanding how well your heart responds to increased oxygen demand during exertion or stress.

Note from MedPark’s Doctors

A nonstress test (NST) evaluates fetal health by examining the fetal heart rate in response to movement. The outcomes are categorizable as reactive or nonreactive. If you have any concerns, it is crucial to communicate your worries or questions with your doctor.