Nonstress test

Nonstress test
Medical diagnostics
Purpose monitors fetal heart rate
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.[1]

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).[2]

Vibroacoustic stimulation can wake the fetus, and is sometimes used to speed up the test or to facilitate further evaluation of a non-reactive nonstress test.[3]

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 and 160 beats per minute with moderate variability (5- to 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.[4] 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.[5]
  • Non-reactive is defined as the presence of less than two fetal heart rate accelerations within a 20-minute period over a 40-minute testing period.[4]

See also

References

  1. ↑ London, Marcia; Ladewig, Patrica; Ball, Jane; Bindler, Ruth (2007). Maternal & Child Nursing Care. Upper Saddle River, NJ: Prentice Hall.
  2. ↑ Smith, C. V.; Nguyen, H. N.; Phelan, J. P.; Paul, R. H. (1986). "Intrapartum assessment of fetal well-being: a comparison of fetal acoustic stimulation with acid-base determinations". Am J Obstet Gynecol. 155: 726–728. doi:10.1016/s0002-9378(86)80007-2.
  3. ↑ Chervenak, Frank A.; Kurjak, Asim (2006). Textbook of Perinatal Medicine, Second Edition (Two Volumes). Informa Healthcare. ISBN 1-84214-333-6.
  4. 1 2 Association of Women’s Health, Obstetric, and Neonatal Nurses (2005). Lyndon, Audrey Lyndon; Ali, Linda Usher, eds. Fetal Heart Monitoring: Principles and Practices (3rd ed.). Dubuque, IA: Kendall/Hunt Publishing Co. ISBN 978-0-7575-6234-1.
  5. ↑ Cousins, L. M.; Poeltler, D. M.; Faron, S.; Catanzarite, V.; Daneshmand, S.; Casele, H. (October 2012). "Nonstress testing at ≤ 32.0 weeks' gestation: a randomized trial comparing different assessment criteria". Am J Obstet Gynecol. Mosby, Inc. 207 (4): 311.e1–311.e7. doi:10.1016/j.ajog.2012.06.032. PMID 23021694.
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