Question

In a non-stress test (NST), all of the following are assessed except?

• A. Variability
• B. Acceleration
• C. Time period
• D. Oxytocin

Hint:

Oxytocin provokes contractions - that belongs to the CST, not the NST.

Answer 1

The Correct Option is D

Step 1: Concept of the NST. The non-stress test is a simple, non-invasive antepartum test that records the fetal heart rate (FHR) using an external transducer for at least 20 minutes. It evaluates fetal well-being by observing the FHR pattern in relation to fetal movements, with no stimulant given to the mother.

Step 2: What the NST actually measures. The trace is read for baseline rate, beat-to-beat variability, the presence of accelerations with fetal movement, and any decelerations, all interpreted over a defined time period (usually a 20 minute window). A reactive (positive) NST shows two or more accelerations of at least 15 beats per minute lasting 15 seconds within 20 minutes.

Step 3: Why oxytocin is the exception. Oxytocin is not part of the NST at all. Giving oxytocin to provoke uterine contractions is the basis of the contraction stress test (CST) or oxytocin challenge test (OCT), which is a different test. Variability, acceleration, and the time period are all components of NST interpretation, so the odd one out is oxytocin.

Hence the correct answer is option 4.