**Core Concept**
Deep transverse arrest refers to a type of labor arrest where the fetal head becomes stuck in the pelvis, with the fetal head being at or below the ischial spines. This occurs when the fetal head is unable to rotate or descend through the pelvis due to various factors such as a small pelvic outlet or a large fetal head.

**Why the Correct Answer is Right**
Deep transverse arrest is most commonly seen in cases where there is a **pelvic contraction**, meaning the pelvic outlet is smaller than the fetal head, making it difficult for the head to pass through. This can be due to a variety of factors such as a **small pelvic inlet**, a **narrow subpubic arch**, or a **small pelvic outlet**. In these cases, the fetal head becomes stuck in the pelvis, leading to a deep transverse arrest.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a **normal pelvis** would not typically cause a deep transverse arrest, as the fetal head would be able to pass through the pelvis with ease.
**Option B:** This option is incorrect because a **large pelvic outlet** would actually make it easier for the fetal head to pass through the pelvis, rather than causing a deep transverse arrest.
**Option C:** This option is incorrect because a **fetal head size** that is within normal limits would not typically cause a deep transverse arrest, as the fetal head would be able to pass through the pelvis with ease.

**Clinical Pearl / High-Yield Fact**
A deep transverse arrest is a type of labor arrest that requires prompt intervention, such as a cesarean section, to prevent fetal distress and other complications.

**Correct Answer: D. Pelvic contraction. Pelvic contraction**