**Core Concept**
Non-engagement at term, also known as delayed umbilical cord separation or non-engagement of the fetal head, refers to a condition where the fetal head fails to descend into the pelvis by the expected time of delivery. In primigravidas (first-time mothers), this can be a significant concern due to the increased risk of complications.

**Why the Correct Answer is Right**
The commonest cause of non-engagement at term in primigravidas is typically **obstructed labor**. Obstructed labor occurs when the fetal head or body cannot move through the birth canal due to various reasons such as cephalopelvic disproportion, fetal malposition, or uterine anomalies. This can lead to a prolonged labor, which may necessitate an emergency cesarean delivery.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that non-engagement at term in primigravidas often requires prompt evaluation and intervention to prevent complications. A thorough assessment of the mother's pelvis, fetal size, and labor progress is essential in determining the best course of action.

**Correct Answer:**
Unfortunately, the options are not provided. However, based on the explanation, the correct answer is **Obstructed Labor**.