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Nonstress Test (NST): Why and How is it Done?

Medically reviewed by Jezreel Esguerra, MD · General Practitioner

Written by Nikita Bhalla · Updated Mar 14, 2023

    Nonstress Test (NST): Why and How is it Done?

    A nonstress test (NST) is a common test a doctor will suggest to a pregnant woman to check the baby’s health.

    In this test, the doctor monitors the baby’s heart rate and movements. The term ‘nonstress’ refers to the fact that nothing is done that creates stress on the baby during the test.

    It is normal to feel a bit stressed before undergoing the test as it gives information about the baby’s heartbeat, oxygen supply, and other aspects. However, you don’t need to worry as your doctor would know various ways that will help keep the baby healthy.

    A nonstress test is recommended when the doctor thinks that there is an increased risk of miscarriage. Your doctor would probably recommend this test after 26 to 28 weeks of pregnancy. 

    Certain nonstress test results or misleading results may indicate that you and your baby need to undergo further testing, monitoring, or special care.

    Why is a nonstress test (NST) done during pregnancy?

    A nonstress test is beneficial as it monitors your baby’s health in the womb.

    This test provides details about the baby’s well-being, his/her oxygen supply, heart rate, and your baby’s movements.

    Normally, a baby’s heart beats faster in the third trimester. However, conditions like fetal hypoxia where the baby does not get enough oxygen may disrupt the response in the test.

    Doctors may recommend this test to specific women. The following is the list of instances when your doctor will recommend NST:

    • Post-term pregnancy or prolonged pregnancy – a pregnancy that gets extended two weeks past the due date.
    • Oligohydramnios – low amniotic fluid.
    • Rh (rhesus) sensitization – a serious condition that can occur, typically during a second or subsequent pregnancy. It is when your red cell antigen blood group is Rh-negative and your baby’s blood group is Rh-positive. 
    • Multiple pregnancies with certain health complications.
    • Underlying health conditions like blood pressure during pregnancy, type 1 diabetes, or heart disease.
    • A baby who has decreased fetal movements or possible fetal growth problems.
    • This test may be done if the doctor suspects any possible pregnancy complications or any growth restrictions affecting the baby in the womb.


    A nonstress test is a non-invasive test. It is a simple test that does not pose any risks to the mother or the baby.

    As it is a simple test, it does not require any special preparation before undergoing one.

    In case you have any doubts, you can ask your doctor. As there are no special preparations for this test, you can confirm this with your doctor.

    Typically, your doctor will voluntarily give instructions for this test, the dos and don’ts that help to achieve proper results.

    Nonstress Test: Understanding the results

    Results of a nonstress test are considered reactive or nonreactive. 

    Reactive NST result

    If your baby’s heartbeat accelerates to a certain level above the normal range for 10 seconds each within a 20-minute window, it is normal. This is considered normal before week 32 of pregnancy.

    At week 32 and above, if your baby’s heartbeat raises to a certain level above the normal range twice or more for at least 15 seconds each within a 20-minute window, it is considered reactive.

    Nonreactive NST result

    If your baby’s heartbeat does not meet the approximate range, the results is nonreactive. 

    Nonreactive results may occur because the baby was asleep or inactive during the time of the test. A reactive NST is considered accurate irrespective of the duration of observation time required.

    However, if the time extends to 40 minutes and your baby’s nonstress test results are nonreactive, your doctor will suggest another prenatal test to check your baby’s health.

    When should it be repeated?

    Your doctor will suggest undergoing a nonstress test if they feel your baby is at increased risk of death in the womb. So to confirm your baby’s well-being and heart rate, your doctor will suggest NST again.

    Also, if you are past due and still haven’t gone into labor, then the gynecologist will get another NST done to check for the baby’s health.

    Nonstress Test


    A nonstress test takes about approximately 20-40 minutes.

    Typically, the nurse will perform the test while your OB-GYN will interpret the results. Your doctor will check your blood pressure before the test and at different intervals throughout testing.

    Next, you will be asked to lie down on a bed or exam table. The nurse will apply a special gel on your abdomen and then attach a transducer around your stomach. This machine helps as an external fetal heart rate monitor that checks your baby’s heartbeat. Also, a uterine monitor is applied to assess for any uterine contractions.

    You may be asked to push a button each time when you feel your baby is moving. You might be provided with a clicker or buzzer to hold in your hand. Each click or buzz will send movement details to a computer monitor.

    If your baby is active at the beginning of the test, your NST will only last about 20 minutes. In case your baby is inactive or sleeping during the test, the test can take a longer time. Also, the nurse will have to wake your baby.

    The nurse may place a noise-making device on your stomach. Additionally, she will provide you with something to eat or drink that will wake up your baby and get him/her active.

    Learn more about staying healthy throughout pregnancy here.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Jezreel Esguerra, MD

    General Practitioner

    Written by Nikita Bhalla · Updated Mar 14, 2023

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