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What is Non-Stress test (NST)?

A non-stress test (NST) is usually performed during the last trimester of pregnancy to measure the heart rate (number of heartbeats per minute), baby movement and reactivity of the heart rate to the movement.  In a majority of cases, heart rate of the foetus increases with its movement. It can be done any time after 26 to 28 weeks depending upon the purpose for which it is performed.

The name non-stress comes from the fact that no external stress is placed on the baby during the test.

  1. Why is Non-Stress test (NST) performed?
  2. How do you prepare for Non-Stress test (NST)?
  3. How is Non-Stress test (NST) performed?
  4. What do Non-Stress test (NST) results mean?
  5. How much does an Non-Stress test (NST) cost?

This test is recommended women with a high-risk pregnancy or those with low-risk pregnancy who have crossed their due date. The doctor may advise NST under the following circumstances:

  • The pregnant woman has diabetes, high blood pressure, clotting disorder, blood disorder, or diseases of the thyroid, kidneys, or heart
  • The baby shows less than normal movement and has slow growth
  • Presence of multiple pregnancies such as twins
  • Presence of excessive amniotic fluid
  • The blood group of the pregnant woman is Rh negative

This test is useful in determining whether the baby is getting enough oxygen and responds to stimuli normally.

Sometimes a biophysical profile is recommended, which includes NST and ultrasound. It helps in the examination of breathing, amniotic fluid quantity, and movement along with the heart rate of the foetus.

No special preparations such as fasting are needed before going for this test.

It is a non-invasive test that does not have any risk for the mother or baby. The number of steps in the procedure may vary between different laboratories, but the common steps of NST include:

  • The pregnant woman is asked to lie down, and jelly is applied to her abdomen
  • A belt is fastened around her abdomen in such a way that the transducer is positioned on foetal heartbeat
  • This is also referred to as external foetal heart rate monitor
  • During this test, the heart rate of the baby is recorded on a monitor as well as on paper
  • The woman is told to press the switch whenever she feels that the baby is moving
  • After the completion of the test, the belt is removed and jelly is wiped off

Sometimes, this test is performed while the baby is sleeping due to which there is minimal movement. In such a case, a unique sound device is employed to wake the foetus and perform the test. This does not cause any harm to the baby but helps the foetus become more active. Consumption of food and drinks by the mother also awakens the foetus.

Results of NST may indicate the following:

Normal results:
If the baby moves twice or more within 20 minutes and foetal heart rate increases with movements during the testing period, the result is said to be reactive or reassuring. A reactive result indicates the absence of any abnormality.

Abnormal results:
It is also called a nonreactive result. The following may be considered abnormalities in NST results:

  • Absence of movements for a test period of 40 minutes is considered abnormal and may indicate several things, one of which is that the baby was asleep during the test
  • If there is no change in foetal heart rate while the foetus moves, this also is abnormal and indicates the necessity of further testing

Results of NST may also be read as Category 1, 2 or 3 as follows:

  • Category 1: indicates a normal result
  • Category 2: indicates the need for further testing or observation
  • Category 3: indicates that the doctor may advise a delivery right away

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.  

The cost of NST in India is between 300 and 600 INR, and it may vary from laboratory to laboratory.

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  1. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Nonstress Testing
  2. Women's health care physicians: The American College of Obstetricians and Gynecologists; Special Tests for Monitoring Fetal Health: FAQ
  3. American Heart Association; All About Heart Rate (Pulse)
  4. American Pregnancy Association; Fetal Non-Stress Test (NST)
  5. Stanford Children's Health: Lucile Packard Children's Hospital, Stanford; Nonstress Testing
  6. Greenberg MB, Druzin ML. Antepartum fetal evaluation. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 11.
  7. Kaimal AJ. Assessment of fetal health. In: Creasy RK, Resnick R, Iams JD, Lockwood CJ, Moore TR, Greene MF, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 7th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 32.
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