Pregnancy is a delicate time; when it is crucial to keep track of self and baby’s well-being. Out of several tests performed for the same, a non-stress test during pregnancy could be suggested by your doctor only when you have some health conditions that may complicate your pregnancy. Non-stress test or NST is a prenatal test used to monitor fetal heart rate for a specific duration. This test is also used during labor to check for the baby’s heartbeat patterns during contractions. Plunge into this post as we bring you important details about this test and when it is suggested during pregnancy.
What Is A Nonstress Test?
A nonstress test, also known as fetal heart rate monitoring, is a simple and non-invasive test performed typically after 28 weeks of pregnancy. It measures the heart rate of the fetus in response to its movements.
The nonstress test is called so because it does not pose any physical stress to you or your fetus (1).
The test may be a simple one, but it is important to track the health of the baby.
Why Would You Need A Nonstress Test?
There are many indications to perform a nonstress test and typically some complication related to pregnancy may warrant the performance of NSTs.
Some reasons why your doctor would recommend the nonstress test are:
- kidney, thyroid or heart disease, high blood pressure or diabetes.
- Your baby’s growth is slow, he or she moves less than usual.
- Your amniotic fluid levels are either too high or too low.
- You had undergone procedures such as external cephalic version or third-trimester amniocentesis.
- You have passed your due date.
- Your baby is diagnosed with any birth defect or abnormality.
- You previously had a miscarriage or stillborn baby.
- You are carrying twins or multiples.
Your doctor might recommend the NST once or twice a week at first, and occasionally later, depending on your and your baby’s condition.
How Is The Nonstress Test Done?
The test is usually performed in a hospital and involves the below procedure.
- Once you lie down on your back, your abdomen is secured with two belts with attached monitors.
- One belt measures the heart rate of your baby while the other measures any uterine contractions you may have.
- You can notice your baby’s movements, which are recorded on the monitor and printed out at the end of the test.
- The graphs on the paper help the doctor assess your baby’s heartbeats during the movements.
- The test lasts for about 20 minutes. If the baby is asleep or inactive, it may be extended by another 20 minutes. Your doctor will try stimulating the baby using an acoustic device that makes a noise and awakens the baby. You may also be told to eat or drink something to make the baby active (3).
Once the test is done, the results are available almost immediately.
What Should You Know About The Nonstress Test Results?
The doctor would use two key phrases to interpret the results:
- Reactive (normal): A normal result, If the fetal heart beats faster (around 15 beats per minute) during a movement of at least 15 seconds, on two separate accelerations in a 20-minute period, the result is reactive (4).
- Non-reactive: There usually is need for further testing. The result is non-reactive when it does not match the criteria mentioned in the first point. While the result is worrisome, a non-reactive result could also be because your baby was asleep or inactive during the process (3).
If the test extends to 40 minutes and the results are non-reactive, the doctor may recommend a follow up ultrasound or even delivery if you are at your due date.If you are not close to completing the full-term, your doctor will conduct some other prenatal tests to assess your baby’s health. The follow-up tests include contraction stress test (CST), biophysical profile (BPP) and modified biophysical profile (MBPP).
- Biophysical profile: This test combines the NST with a fetal ultrasound. It assesses the baby’s breathing, movements, muscle tone and amniotic levels. The test results can be normal, abnormal or sometimes unclear. If heartbeat results are abnormal, you should go for early delivery, and if the results are unclear, you will have a retest.
- Modified biophysical profile: MBPP is also an NST along with an ultrasound that only looks for the amniotic fluid levels. This test is enough to determine the baby’s health and takes lesser time than a BPP (1).
A nonstress test monitors the fetal heart rate for a specific duration. It is non-invasive and is performed to ascertain the health of your baby to identify complications that may arise due to conditions such as high BP, gestational diabetes, abnormal amniotic fluid volume, history of miscarriages, or multiple pregnancies. It is performed at around 28 weeks of gestation and has no adverse effects on you or the baby. Do not hesitate to talk to your doctor before the test to allay any fears.