How long must an early deceleration last from onset to nadir?

An early deceleration is characterized by a gradual decrease in fetal heart rate (FHR) that begins with a contraction and returns to the baseline as the contraction ends. For an early deceleration to be classified correctly, it generally must last for a duration of more than 30 seconds from the onset to the nadir. This timeframe allows for the appropriate identification of the deceleration pattern, which is typically related to uterine contractions and indicates a physiological response to increased pressure on the fetal head during labor.

The understanding of this timing is crucial for healthcare professionals to correctly interpret fetal monitoring data and to distinguish early decelerations from other types of decelerations, such as variable or late decelerations, which have different implications for fetal well-being. Recognizing the duration helps in evaluating the situation and making decisions that affect both maternal and fetal outcomes.