Girish Mahajan (Editor)

Nonstress test

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ICD-9-CM
  
75.34

A nonstress test (NST) is a screening test used in pregnancy. A cardiotocograph is used to monitor the fetal heart rate.

Contents

Premise

The premise of the NST is that a well-oxygenated, non-acidemic fetus will spontaneously have temporary increases in the fetal heart rate (FHR).

Vibroacoustic stimulation can wake the fetus, and is sometimes used to speed up the test or to facilitate further evaluation of a nonreactive nonstress test.

Interpretation

A nonstress test can be classified as normal, atypical, or abnormal. A normal nonstress test will show a baseline fetal heart rate between 110-160 beats per minute with moderate variability (5-25 interbeat variability) and 2 qualifying accelerations in 20 minutes with no decelerations.

Previous terminology: Reactive/non-reactive:

  • Reactive (normal) is defined as the presence of two or more fetal heart rate accelerations within a 20-minute period, with or without fetal movement discernible by the pregnant woman. Accelerations are defined as 15 bpm above baselines for at least 15 seconds if beyond 32 weeks gestation, or 10 bpm for at least 10 seconds if at or below 32 weeks.
  • Nonreactive is defined as the presence of less than two fetal heart rate accelerations within a 20-minute period over a 40-minute testing period.

    • References

    Nonstress test Wikipedia
    (Text) CC BY-SA