A prolonged deceleration can be defined as:

• A. An abrupt decrease in FHR below the baseline of at least 15 beats/min lasting 15 seconds to 2 minutes
• B. An abrupt decrease in FHR below the baseline of at least 15 beats/min lasting 2 to 10 minutes
• C. An abrupt decrease in FHR below the baseline of at least 15 beats/min lasting over 10 minutes
• D. An abrupt decrease in FHR below the baseline of at least 15 beats/min lasting less than 15 seconds

Answer: (B)

Prolonged deceleration is a sustained drop in fetal heart rate of at least 15 beats per minute below the baseline that lasts between 2 and 10 minutes. That duration is the key differentiator: shorter than 2 minutes are brief decelerations, while lasting more than 10 minutes is considered a change in the baseline rather than a deceleration. The decrease is described as abrupt in onset, but the defining feature here is the 2–10 minute window. This distinction helps separate prolonged decelerations from other patterns (early, late, or variable decelerations), which are categorized mainly by when they occur in relation to contractions rather than by how long they last.