Variable decelerations are caused by which mechanism?

Variable decelerations are caused by which mechanism?

• A. Compression of the umbilical cord causing a drop in fetal heart rate
• B. Uteroplacental insufficiency causing late decelerations
• C. Maternal hypotension causing tachycardia
• D. Fetal tachyarrhythmia

Answer: (A)

Variable decelerations reflect abrupt drops in fetal heart rate caused by compression of the umbilical cord. When the cord is squeezed, blood flow to the fetus is transiently reduced, triggering a quick vagal response that lowers the heart rate. As the compression releases, the heart rate returns to baseline promptly. These decelerations are characteristically abrupt and can vary in timing and depth, often appearing as a sharp “V” or “U” shaped dip on the tracing, not tied to contractions. This differs from late decelerations, which follow contractions and indicate uteroplacental insufficiency, and from patterns caused by maternal hypotension or fetal tachyarrhythmias, which have different patterns and mechanisms.

Variable decelerations reflect abrupt drops in fetal heart rate caused by compression of the umbilical cord. When the cord is squeezed, blood flow to the fetus is transiently reduced, triggering a quick vagal response that lowers the heart rate. As the compression releases, the heart rate returns to baseline promptly. These decelerations are characteristically abrupt and can vary in timing and depth, often appearing as a sharp “V” or “U” shaped dip on the tracing, not tied to contractions.

This differs from late decelerations, which follow contractions and indicate uteroplacental insufficiency, and from patterns caused by maternal hypotension or fetal tachyarrhythmias, which have different patterns and mechanisms.