In a nonstress test (NST) for a fetus at 34 weeks, what is considered a normal or reactive acceleration?

In a nonstress test (NST), a reactive acceleration indicates that the fetal heart rate shows appropriate responses to fetal movement, signaling a well-oxygenated fetus and a healthy environment. The criteria for a normal or reactive NST are defined as an increase in heart rate of at least 15 beats per minute (bpm) above the baseline, lasting for at least 15 seconds.

At 34 weeks of gestation, the fetus is sufficiently developed to demonstrate these characteristics. Therefore, the correct option describes an acceleration of 15 bpm for 15 seconds. This 15/15 rule serves as a standard indicator of fetal well-being during the NST.

Other options include various combinations of bpm and duration that do not align with the established guidelines for a reactive NST. For example, while larger accelerations (like 20 bpm or more) may indicate good fetal health, the key criteria focus on the minimum threshold needed to classify the test as reactive. Hence, the most appropriate choice for what constitutes a normal or reactive acceleration in this context is indeed the increase of 15 bpm over a duration of 15 seconds.