**Core Concept**
Knots in the umbilical cord are a significant issue during fetal development, resulting from the entanglement of umbilical cord vessels. This phenomenon is associated with an increased risk of fetal distress, growth restriction, and even stillbirth. The pathogenesis of knots in the umbilical cord involves the twisting of the cord around its own axis, leading to compression of the blood vessels.

**Why the Correct Answer is Right**
The umbilical cord contains two arteries and one vein, which are responsible for supplying oxygen and nutrients to the fetus and removing waste products. When knots form in the umbilical cord, they can compress these vessels, leading to decreased blood flow to the fetus. This compromise in fetal circulation can result in significant morbidity and mortality. The presence of knots in the umbilical cord is often associated with an increased risk of fetal distress, which can be detected through ultrasound examination and monitoring of fetal heart rate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the underlying mechanism of knot formation in the umbilical cord. While torsion of the cord may contribute to knot formation, it is not the primary cause.
**Option B:** This option is incorrect because it does not address the pathophysiology of knot formation in the umbilical cord. The presence of knots in the cord is not simply a matter of cord length or fetal movement.
**Option C:** This option is incorrect because it does not provide a clear explanation for the increased risk of fetal distress associated with knots in the umbilical cord. While cord compression may contribute to fetal distress, it is not the only factor.

**Clinical Pearl / High-Yield Fact**
Knots in the umbilical cord are a significant risk factor for fetal distress and stillbirth. Ultrasound examination and monitoring of fetal heart rate are essential for detecting fetal compromise in the presence of umbilical cord knots.

**Correct Answer:** D.