A primigravid client is admitted to the maternity ward in spontaneous active labor at term. A continuous electronic fetal monitor is applied to evaluate fetal well-being. Throughout the observation period, the tracing displays multiple episodes where the fetal heart rate abruptly decreases by 20 to 30 beats per minute from a stable baseline of 145 beats per minute. These abrupt drops reach their nadir within 15 seconds, last for approximately 30 to 40 seconds, and then rapidly return to the baseline. The decreases occur inconsistently, showing no uniform relationship to the onset or peak of the concurrent uterine contractions. Which of the following is the most likely underlying physiological cause of this fetal heart rate pattern?
- Compression of the umbilical cordCevap
- BInsufficient uteroplacental blood flow
- CCompression of the fetal head
- DPhysiologic fetal sleep state
- EMaternal systemic inflammatory response
Cevap
Compression of the umbilical cord
The correct answer is compression of the umbilical cord. The clinical vignette describes a classic pattern of variable decelerations. These are defined as abrupt decreases in the fetal heart rate (onset to nadir in less than 30 seconds) of at least 15 beats per minute, lasting at least 15 seconds, followed by a rapid return to the baseline. Unlike early or late decelerations, variable decelerations vary in their onset, depth, and duration, and they do not have a uniform relationship to uterine contractions. The physiological mechanism behind variable decelerations is the temporary compression of the umbilical cord, which acutely increases fetal peripheral vascular resistance. This triggers a baroreceptor-mediated vagal response that abruptly slows the fetal heart rate.
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Anahtar Kavram
Interpretation of intrapartum fetal heart rate monitoring, specifically identifying variable decelerations and their etiology.