Which fetal heart rate pattern most signifies fetal distress during labor?

The pattern that most signifies fetal distress during labor is characterized by nonremedial late decelerations, which are defined as a gradual decrease in the fetal heart rate that occurs after a contraction and does not return to the baseline until after the contraction has ended. A heart rate dropping to between 60-80 bpm indicates significant cardiovascular compromise for the fetus. This pattern suggests that the fetus may not be tolerating labor well, likely due to a decrease in uteroplacental blood flow, which can be associated with conditions such as uterine hypotonia, placental insufficiency, or cord compression.

In contrast, variable decelerations can occur with changes in maternal position, often indicating umbilical cord compression, and may resolve quickly with repositioning, implying they are not necessarily associated with acute distress. Early decelerations typically reflect fetal head compression during contractions but usually indicate a reassuring response and resolve quickly without significant implication of distress. A steady baseline heart rate of 140 bpm is typically considered normal and does not signal distress; rather, it suggests that the fetus is stable.

Thus, the presence of late decelerations, particularly at such a low heart rate, is a critical indicator of fetal distress that requires immediate assessment and intervention.