What defines a reactive non-stress test (NST)?

A reactive non-stress test (NST) is characterized by the presence of two or more fetal heart rate accelerations within a 20-minute period. This indicates that the baby's heart is responding normally to movements, which is a positive sign of fetal well-being. The accelerations are typically defined as increases in heart rate of at least 15 beats per minute above the baseline for at least 15 seconds. This response suggests that the fetus is getting adequate oxygen and is not experiencing any distress.

In contrast, the other options do not align with the criteria for a reactive NST. For instance, having one acceleration does not meet the threshold for a reactive result, and no accelerations within a specified time frame indicate a non-reactive test, which could suggest fetal distress or compromised well-being. A declining fetal heart rate over time would also be concerning and indicative of potential fetal distress rather than a normal, reactive response. Thus, the correct answer highlights the specific criteria that reflect a healthy status for the fetus during the test.