The correct answer is choice D. Severe variable decelerations indicate cord compression and hypoxemia in a fetus with a prolapsed umbilical cord. Variable decelerations are abrupt decreases in fetal heart rate below the baseline, usually associated with uterine contractions. Severe variable decelerations are defined as having a nadir of less than 70 beats per minute or lasting longer than 60 seconds.

Choice A is wrong because episodic accelerations are transient increases in fetal heart rate above the baseline, usually indicating fetal well-being.

Choice B is wrong because fibrillation is an irregular and rapid contraction of the atria of the heart, which is not a normal fetal heart rate pattern.

Choice C is wrong because moderate tachycardia is a slightly elevated fetal heart rate above the normal range of 110 to 160 beats per minute, which may be caused by maternal fever, fetal infection, fetal anemia, or fetal hypoxia.

However, moderate tachycardia alone does not indicate cord compression and hypoxemia.

The normal range of fetal heart rate is 110 to 160 beats per minute.