A nonstress test (NST) is a prenatal test used to check the well-being of the unborn baby. During an NST, the baby’s heart rate and movements are monitored. This test allows your doctor to see how well your baby is doing and whether or not they are under stress.
If you are pregnant, it’s important to know what to expect during an NST. In this blog post, we will discuss everything you need to know about nonstress tests.
What is a nonstress test?
A nonstress test is a type of fetal assessment that checks how your baby’s heart responds to changes in their movement. It’s done during the last few weeks of pregnancy and can help your doctor check your baby’s health.
A nonstress test is a noninvasive test that doesn’t pose any physical risks to you or your baby.
A nonstress test is typically advised when a physician believes the baby is at an increased risk of dying. It may be conducted after 26 to 28 weeks into pregnancy. Some nonstress test findings might suggest that you and your baby require further monitoring, testing, or specialized treatment.
Why is a nonstress test done?
It is usually done for monitoring fetal health. A nonstress test aims to provide helpful information about your baby’s oxygen supply by checking their heart rate and how it responds to your baby’s movement.
The main purpose of a nonstress test is to check how your baby’s heart reacts to its movement. In a normal pregnancy, a baby will move around frequently. These movements can cause the baby’s heart rate to speed up and then slow down again.
The test monitors the baby’s heart rate to see how it responds to these movements. The test can help your doctor check your baby’s health and well-being. It can also help them check for any problems with the baby’s heart or blood flow. Your health care provider might recommend a nonstress test if you have:
- Multiple pregnancies with certain complications
- A medical condition, such as diabetes
- High blood pressure
- Certain genetic conditions
- Complications in a previous pregnancy
- A baby has decreased fetal movements
- Low amniotic fluid (oligohydramnios)
How is a nonstress test performed?
A nonstress test is usually done at the healthcare provider’s office or in the hospital.
Before the procedure
Before the nonstress test begins, your blood pressure will be assessed.
During the procedure
During the nonstress test, you’ll be asked to lie on your back on an exam table. Then, your health care provider will place two belts around your abdomen.
One of the belts will have a monitor that records your baby’s heartbeat and movement. The other belt will record contractions. The mother is asked to press the button when she feels the baby move. The blood pressure of the mother is checked at regular intervals.
You’ll be asked to relax and let the test proceed. The test usually takes about 20 to 30 minutes. In some cases, the testing occurs during a baby’s sleep cycle, when there is little fetal movement. If the baby does not awake, he/she can be awakened by using a loud noise, a light on the mother’s abdomen, or touching the abdomen with hands.
After the procedure
After the test, your health care provider will review the results with you. They’ll discuss any next steps that might be needed based on the findings.
The test results are given in terms of how the fetal heart rate reacts to changes in the baby’s activity level. Test results of the nonstress test may be:
The test is considered reactive or re-assuring if the heart rate increases by at least 15 beats per minute for at least 15 seconds within a 20-minute window. This means the baby’s heart rate increased two or more times during the testing period.
At 32 weeks of pregnancy or later, if your baby’s heartbeat speeds to a certain level above the baseline twice or more for at least 15 seconds each within a 20-minute window, the results are considered reactive.
A non-reactive or non-assuring result is given when the fetal heart rate fails to increase by at least 15 beats per minute in response to fetal movement.
If the test is non-reactive, your doctor will likely order additional testing, such as a biophysical profile, contraction stress test, or amniocentesis, to confirm the results. If the test is reactive, it usually means that the baby is doing well and no further testing is needed.
The non-stress test is considered a screening tool, which means that it can help to identify high-risk pregnancies. However, the test is not diagnostic, which means that it cannot be used to definitively diagnose a problem. Your healthcare provider will tell you if you need another prenatal testing.
What are the risks of a nonstress test?
A nonstress test is generally safe and doesn’t pose any risks to you or your baby. However, in some rare cases, the test can cause false readings. This might lead to unnecessary tests or treatments.
You might experience some discomfort from lying on your back for an extended period. You might also feel mild pressure from the belts around your stomach.
If you have any concerns about the test, be sure to talk to your health care provider.
What happens if the nonstress test is abnormal?
If the nonstress test is abnormal, it doesn’t necessarily mean that there’s a problem with your baby. In some cases, an abnormal result may be caused by factors such as:
- Fetal sleep
- Fetal positioning
- Maternal anxiety
In these cases, your health care provider may recommend a repeat test. If the second test is also abnormal, further testing may be needed to check your baby’s health. This might include tests such as an umbilical artery doppler or biophysical profile.
These tests can help your doctor check the baby’s blood flow and movements. They can also help rule out any other potential problems.