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Question

Difficulty: MediumLabor, Delivery, and Puerperium

Match each intrapartum fetal heart rate (FHR) abnormality with its primary underlying physiologic or pathophysiologic mechanism.

  • Early decelerationsFetal head compression causing vagal nerve stimulation
  • Variable decelerationsUmbilical cord compression causing a baroreceptor-mediated reflex
  • Late decelerationsUteroplacental insufficiency leading to transient fetal hypoxemia
  • Sinusoidal patternSevere fetal anemia or profound hypoxia with loss of autonomic control
  • Prolonged decelerationAcute, sustained disruption of fetal oxygenation (e.g., uterine rupture, maternal hypotension)

Answer

Early decelerations match with fetal head compression. Variable decelerations match with umbilical cord compression. Late decelerations match with uteroplacental insufficiency. Sinusoidal patterns match with severe fetal anemia. Prolonged decelerations match with acute, sustained oxygenation disruption.
Accurate interpretation of fetal heart rate monitoring requires linking the visible pattern to its physiologic cause. Early decelerations align perfectly with contractions due to head compression. Variable decelerations are abrupt, reflecting the sudden mechanical nature of cord compression. Late decelerations are delayed, reflecting the time it takes for a contraction to restrict blood flow enough to trigger fetal chemoreceptors. Sinusoidal patterns reflect a loss of the normal autonomic baseline control, seen in severe anemia. Prolonged decelerations represent a sustained hypoxic insult.

Step-by-Step Solution

1
Analyze the morphologic characteristics (abrupt vs. gradual, timing relative to contractions) of each fetal heart rate pattern.
Differentiate between early, late, and variable decelerations based on their onset, nadir, and relationship to the uterine contraction cycle.
The precise timing and shape of the deceleration directly point to the underlying autonomic reflex or hypoxic mechanism.
2
Correlate unique or extended patterns (sinusoidal, prolonged) with their specific severe or acute pathophysiologic states.
Identify that a smooth undulating wave indicates anemia or severe hypoxia, while a deceleration lasting over 2 minutes indicates a sustained and potentially catastrophic hypoxic event.
These specific patterns represent severe compromise rather than transient, expected responses to individual contractions.

Key Concept

Fetal heart rate deceleration mechanisms
Estimated Time:1m 30s
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Topics

Labor, Delivery, and Puerperium

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