Nonstress Test

What is a nonstress test?

A nonstress test (NST) during pregnancy looks at how your baby’s heart rate responds to movement. The prenatal test can help your provider ensure your baby is receiving enough oxygen and that the nervous system is functioning well.

In most cases, a baby’s heart rate will increase with movement. This simple, painless screening test can’t diagnose conditions, but it’s often used in the third trimester to check your baby's well-being. The NST is noninvasive and doesn’t cause any stress to your baby, hence its name. The monitor simply observes the baby’s natural activity and responses in utero.

There are many reasons we might recommend doing an NST, so don’t be concerned if your provider recommends one. It’s simply a tool to monitor your baby’s heart rate. More tests are needed to make a diagnosis. The obstetric experts at The Ohio State University Wexner Medical Center in Columbus, Ohio, will help you make sense of any abnormal results and will provide follow-up care, if needed.

What does a nonstress test evaluate?

An NST provides valuable insight into how well your baby is doing in utero, both for you as a parent and for your health care team. Evaluating how a baby’s heart rate responds to movement will help us assess the baby’s oxygen levels, nervous system development and overall well-being.

The NST offers reassurance that the baby is active as expected. Confirming that a baby’s heart rate increases with movement is a healthy sign that the placenta is providing adequate support.

Here’s the data your provider observes during an NST:

Heart rate pattern: Whether it accelerates appropriately with movement
Variability: How much the heart rate fluctuates from beat to beat
Baseline heart rate: The baby’s average heart rate at rest
Response to contractions: If you do have contractions

Together, these observations help providers determine if your baby is thriving or needs closer monitoring, additional testing (such as a biophysical profile), or early delivery for safety.

Why do I need a nonstress test?

You may schedule an NST for a variety of reasons, most commonly if you haven’t felt your baby kick or move for a while. The prenatal screening is typically only done in the third trimester. Your provider may recommend an NST with an ultrasound as part of a biophysical profile prenatal test, which also is used to monitor your baby’s well-being.

Reasons a stress test might be recommended include:

Your pregnancy has gone two weeks past your due date.
Your baby is moving less than usual.
Your baby is measuring small.
You’re carrying multiple babies.
You have an underlying medical condition, like type 1 diabetes or high blood pressure.
You have low amniotic fluid.
You’ve had a stillborn baby or pregnancy complications in the past.

What can I expect at my nonstress test?

A nonstress test is typically performed on an outpatient basis at a doctor’s office. During the test, you’ll recline comfortably while two soft belts with sensors are placed around your belly. This is similar to the monitoring you’ll receive in labor.

One belt records your baby’s heart rate.
The other measures uterine contractions or fetal movement.

Next, you’ll be asked to keep track of the baby’s movements. You may be asked to press a button each time you feel the baby move. The test typically lasts about 20 minutes but might take up to 40 minutes if your baby is resting or asleep.

If you have a high-risk pregnancy, your provider might recommend an NST once or twice a week after 32 weeks, unless indicated prior. Since the procedure has no physical risks, it’s a great tool to give us information on the baby and guide us in changes we may need to make for your care plan.

Results of the nonstress test

Results of a nonstress test should be available immediately and are categorized as either reactive (normal) or nonreactive. It’s important to remember that this test is only a screening tool to determine if further evaluation is necessary. That means the results aren’t always able to predict outcomes, whether good or bad.

What is a reactive nonstress test?

A reactive nonstress test means:

Between 28 and 32 weeks, results are normal if your baby’s heartbeat rises to a certain amount twice for 10 seconds over 20 minutes.
After 32 weeks, results are normal if your baby’s heartbeat rises a certain amount twice for 15 seconds over 20 minutes.
Sometimes, the test will be extended to 40 minutes. It doesn’t matter how long it takes within that window for the baby to reach the criteria for the results to be considered normal.

What is a nonreactive nonstress test?

A nonreactive nonstress test means:

We didn’t see a rise in heart rate when your baby moved.
We might suggest another prenatal test to further examine what might be happening with your baby. These could include a biophysical profile, which combines a nonstress test and an ultrasound, or a contraction stress test, which looks at how the baby reacts to uterine contractions.

Additionally, a nonstress test can identify decelerations, which are drops in the baby’s heart rate. There are different types of deceleration and causes for it. We might suggest additional monitoring or premature delivery, depending on the situation.

Why choose Ohio State for your nonstress test?

Maternal Fetal Medicine specialists at the Ohio State Wexner Medical Center are specially trained to handle all pregnancies, including the most complex cases. Our high-risk pregnancy team ensures that families dealing with prenatal issues receive the proper care and support needed to deliver their babies safely.

We use advanced monitoring technology to evaluate your baby’s health and provide you with peace of mind throughout pregnancy. Our prenatal testing services, including NST tests, are performed in safe, comfortable and compassionate settings. Our physician-directed genetic counselors are experts at providing personalized, comprehensive genetic counseling, education and fetal treatment options.