The duration of a contraction is measured from:

The duration of a contraction is determined by measuring the time from the beginning of the contraction to its end. This measurement reflects the entire period during which the uterus is contracting, which is crucial for assessing the labor progress and the baby's well-being.

By observing the full span of the contraction, healthcare providers can evaluate its effectiveness and the overall pattern of contractions during labor. Monitoring this duration helps in understanding how well the uterus is working to facilitate the labor process and can indicate if there's a need for further medical intervention.

Other options do not accurately capture the definition of contraction duration. For example, measuring from the peak to the baseline pertains to amplitude, while the timing from one contraction to the next focuses on frequency, and every interval of contractions is more about rhythm rather than the duration of a single contraction. Hence, recognizing the correct definition as the time from the beginning to the end of a contraction is essential in fetal heart monitoring and labor management.