What is the most common cause of variable decelerations in fetal heart rate?

The correct answer is choice B. Umbilical cord compression.Variable decelerations are the most common type of fetal deceleration and they are caused by compression of the umbilical cord.They vary in shape, duration, and intensity and may not have a constant relationship with uterine contractions.

Choice A is wrong because uteroplacental insufficiency is the cause of late decelerations, not variable decelerations.Uteroplacental insufficiency is a decrease in the blood flow to the placenta that reduces the amount of oxygen and nutrients transferred to the fetus.

Choice C is wrong because maternal hypotension is one of the possible causes of late decelerations, not variable decelerations.Maternal hypotension can reduce the uteroplacental blood flow and cause fetal hypoxia.

Choice D is wrong because fetal head compression is the cause of early decelerations, not variable decelerations.Early decelerations are benign and uniform in shape and they occur when the fetal head is pressed against the cervix during a uterine contraction.

The correct answer is choice D. A loop of umbilical cord protruding from her vagina.This is a sign of umbilical cord prolapse, which is a medical emergency that occurs when the cord slips past the fetal presenting part and becomes compressed, reducing blood flow and oxygen to the fetus.The nurse should immediately call for help, place the woman in a knee-chest or Trendelenburg position, insert two fingers into the vagina and lift the presenting part off the cord, cover the cord with sterile saline-soaked gauze, administer oxygen, and prepare for an emergency cesarean delivery.

Choice A is wrong because a sudden increase in fetal heart rate variability is not a specific sign of cord prolapse.It may indicate fetal well-being or distress depending on the pattern and duration of the variability.

Choice B is wrong because a large amount of clear amniotic fluid is not a sign of cord prolapse.It may indicate rupture of membranes, which is a risk factor for cord prolapse if the presenting part is not engaged.

Choice C is wrong because a change in fetal heart rate from 140 to 90 bpm is not a sign of cord prolapse.It may indicate fetal bradycardia, which can have many causes such as hypoxia, acidosis, medication effects, or fetal sleep cycle.