Final answer:
The common cause of variable decelerations in fetal heart rate during labor is umbilical cord compression, requiring careful monitoring to ensure fetal well-being.
Step-by-step explanation:
The common etiology of a variable deceleration in an external fetal monitor for a laboring woman is umbilical cord compression. Variable decelerations are sudden drops in the fetal heart rate, which can vary in duration, intensity, and timing relative to uterine contractions.
These decelerations are primarily associated with the compression of the umbilical cord, which can reduce blood flow and oxygen delivery to the fetus. This condition requires careful monitoring as it can indicate that the fetus is experiencing distress. In contrast, fetal head compression is more commonly associated with early decelerations, while uteroplacental insufficiency and maternal hypotension are typically linked to late decelerations.