**Core Concept**
Ovarian tumors can be prone to torsion, especially during pregnancy, due to the increased size and mobility of the uterus. Torsion occurs when the ovary becomes twisted, cutting off its blood supply and leading to severe pain and potentially life-threatening complications.

**Why the Correct Answer is Right**
Dermoid cysts, also known as mature teratomas, are a type of germ cell tumor that are more common in younger women. They are composed of various tissues such as hair, muscle, and teeth, and can grow to be quite large. During pregnancy, the increased size and mobility of the uterus can cause the dermoid cyst to become twisted, leading to torsion. This is because dermoid cysts are often pedunculated, meaning they have a stalk-like structure that can twist and cut off blood supply.

**Why Each Wrong Option is Incorrect**
**Option A:** Serous cystadenomas are a type of epithelial tumor that are more common in older women. They are usually unilocular and less likely to become twisted during pregnancy.

**Option B:** Mucinous cystadenomas are also a type of epithelial tumor that are more common in older women. They are often large and multilocular, but are less likely to become twisted during pregnancy due to their firm consistency.

**Option D:** Theca lutein cysts are a type of hyperplastic ovarian cyst that occur in response to high levels of hCG, often seen in conditions such as gestational trophoblastic disease. They are usually bilateral and less likely to become twisted during pregnancy.

**Clinical Pearl / High-Yield Fact**
Dermoid cysts are more common in women of reproductive age and are often associated with a history of previous pelvic surgery or pelvic inflammatory disease. They can also be associated with an increased risk of ovarian cancer.

**Correct Answer Line**
✓ Correct Answer: C. Dermoid cyst