Non-stress test is said to be normal if there are?

JODHPUR AIIMS SNO-2018

Obstetrics & Gynaecology

Easy

Appeared in: JODHPUR AIIMS SNO-2018

Explanation

A normal or reassuring Non-Stress Test (NST) is referred to as 'reactive'.
The primary criterion for a reactive NST is the presence of two or more fetal heart rate (FHR) accelerations within a 20-minute observation period.
For a fetus at 32 weeks' gestation or older, an acceleration is defined as an increase in FHR of at least 15 beats per minute (bpm) above the baseline that lasts for at least 15 seconds.
The presence of these accelerations is a strong indicator of adequate fetal oxygenation and a healthy, intact central nervous system.

Option B: While an NST is often extended to 40 minutes if the initial 20 minutes are non-reactive (to account for fetal sleep cycles), the standard definition of a reactive test is based on achieving the criteria within a 20-minute window.
Option C: The defining feature of a reactive NST is the presence of accelerations, not the absence of decelerations. A test can have no decelerations but still be non-reactive (abnormal) if there are no accelerations.
Option D: This describes a 'non-reactive' NST, which is an abnormal finding. The absence of accelerations indicates that the fetus is not demonstrating the expected heart rate response to movement.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of Non-Stress Test (NST) results as background academic context rather than a clinical decision trigger.
The NST is a cornerstone of antepartum fetal surveillance used to assess fetal well-being, particularly in high-risk pregnancies such as those complicated by diabetes, hypertension, or post-term gestation.
A reactive NST is highly reassuring, indicating a low risk of fetal death within the next week.
A non-reactive NST is not always a sign of fetal distress; it can be caused by a fetal sleep cycle. The standard procedure is to extend the test to 40 minutes. If it remains non-reactive, further investigation with a biophysical profile (BPP) or contraction stress test (CST) is necessary.

How to Approach the Question

First, identify the keywords in the question: 'Non-stress test' and 'normal'. This signals that the question is asking for the definition of a reactive NST.
Recall the specific criteria for a reactive NST. The most important parameters are the number of accelerations and the time frame.
Remember the standard '2 in 20' rule: at least two qualifying FHR accelerations in a 20-minute period.
Evaluate the options based on this rule. Option A directly matches this definition.
Differentiate this from Option B by remembering that the 40-minute period is an extension for an initially non-reactive test, not the primary definition itself.
Eliminate Option C because the presence of accelerations is the key positive finding, not just the absence of decelerations.

Concept Tested & Keywords

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E6 Obstetrics Williams p. 70-93