**Core Concept**
Mouret's sign, also known as the "Mouret's sign of uterine inversion," is a clinical indicator of uterine inversion, which is a condition where the uterus turns inside out during childbirth. This sign is crucial for diagnosing uterine inversion, which can lead to severe complications if left untreated.

**Why the Correct Answer is Right**
Mouret's sign is characterized by a visible, rounded appearance of the uterine fundus below the umbilicus, which is a result of the uterus being inverted. This occurs when the uterus is compressed and inverted, causing it to move into the cervix and vagina. The compression of the uterine vessels leads to a decrease in blood flow, resulting in the characteristic rounded appearance of the fundus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Mouret's sign is specific to uterine inversion and is not associated with other conditions such as uterine prolapse or ovarian torsion.
**Option B:** This option is incorrect because Mouret's sign is not a radiological finding but rather a clinical indicator of uterine inversion.

**Clinical Pearl / High-Yield Fact**
Mouret's sign is a critical clinical indicator of uterine inversion, and prompt recognition of this sign is essential for prompt treatment and prevention of severe complications.

**Correct Answer: C. Uterine inversion.**