What defines a reactive NST?

• A. 2 accelerations of 15 bpm for 15 seconds within 20 minutes
• B. No accelerations within 40 minutes
• C. One acceleration of 20 bpm for 10 seconds
• D. Continuous baseline variability

Answer: (A)

A reactive NST means the fetus shows enough heart-rate accelerations in response to movement, indicating good autonomic function and likely adequate oxygenation. An acceleration is a rise in fetal heart rate of at least 15 beats per minute above baseline and lasting at least 15 seconds. For the test to be considered reactive, you must observe two such accelerations within a 20-minute period. This pattern demonstrates the fetus can respond appropriately to stimuli.

If there are no accelerations within 40 minutes, or only one acceleration occurs, the NST is nonreactive because it fails to meet the required two accelerations in 20 minutes. Baseline variability by itself isn’t what defines reactivity; accelerations are the key indicator.