## **Core Concept**
Nonengagement of the fetal head at term in a primigravida refers to the failure of the fetal head to move down into the pelvis. This condition is often related to the size and shape of the pelvis, the size of the fetal head, and the presence of any obstructing factors.

## **Why the Correct Answer is Right**
The correct answer, **C. Cephalopelvic disproportion (CPD)**, is the most common cause of nonengagement at term in primigravidas. CPD occurs when the fetal head or body is too large to pass through the mother's pelvis. This condition can be due to a variety of factors including a small maternal pelvis, a large fetus, or an abnormally shaped pelvis. The mechanism involves a mismatch between the fetal size and the maternal pelvic dimensions, preventing the fetal head from engaging in the pelvis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while it might represent a potential cause, it is not specified and therefore cannot be evaluated.
- **Option B:** This option is incorrect as it is also unspecified and does not directly relate to known causes of nonengagement.
- **Option D:** This option is incorrect because, although uterine anomalies can cause issues during pregnancy and labor, they are not the most common cause of nonengagement at term.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that cephalopelvic disproportion (CPD) is a leading cause of obstructed labor and can necessitate interventions such as cesarean delivery. Assessment of CPD involves evaluating the maternal pelvis and estimating fetal weight.

## **Correct Answer:** C. Cephalopelvic disproportion.