Match each intrapartum fetal heart rate (FHR) tracing description with its primary pathophysiologic mechanism.
- Abrupt decreases in FHR (onset to nadir < 30 seconds), not necessarily associated with contractionsTransient umbilical cord compression causing fetal systemic hypertension and a baroreceptor-mediated vagal response
- Gradual decreases in FHR (onset to nadir ≥ 30 seconds), with the nadir occurring after the peak of the contractionUteroplacental insufficiency causing transient fetal hypoxemia and a chemoreceptor-mediated response
- Gradual decreases in FHR (onset to nadir ≥ 30 seconds), with the nadir mirroring the peak of the contractionFetal head compression causing altered cerebral blood flow and a benign reflex vagal response
- Smooth, sine-wave-like undulating FHR baseline with a frequency of 3-5 cycles per minute and absent variabilityProfound fetal anemia causing tissue hypoxia and loss of autonomic nervous system modulation
Answer
1) Abrupt decreases match with transient cord compression. 2) Gradual decreases delayed after the contraction peak match with uteroplacental insufficiency. 3) Gradual decreases mirroring the contraction match with fetal head compression. 4) Sinusoidal pattern matches with profound fetal anemia.
Correctly identifying fetal heart rate patterns requires evaluating the onset, depth, and timing relative to uterine contractions. Variable decelerations are abrupt and caused by cord compression. Late decelerations are gradual, delayed relative to contractions, and caused by uteroplacental insufficiency. Early decelerations are gradual, mirror contractions, and are caused by head compression. A sinusoidal pattern lacks variability and indicates severe fetal anemia.
Step-by-Step Solution
Key Concept
Pathophysiology and recognition of intrapartum fetal heart rate decelerations and specific patterns.