**Core Concept**
The patient's presentation is consistent with a common, self-limiting condition affecting the oral mucosa during pregnancy, characterized by the formation of a nodule or lesion. This condition is related to the physiological changes and hormonal fluctuations that occur during pregnancy.

**Why the Correct Answer is Right**
The patient's symptoms and physical examination findings are indicative of a pyogenic granuloma, also known as a pregnancy tumor. This condition is thought to be caused by the increased levels of estrogen and progesterone during pregnancy, leading to vasodilation and increased vascular permeability. The resulting nodule is a benign, inflammatory lesion composed of granulation tissue, which is rich in blood vessels and inflammatory cells. The condition typically resolves spontaneously after delivery, as the hormonal changes that triggered it are reversed.

**Why Each Wrong Option is Incorrect**
**Option A:** A fibroma is a type of benign tumor that arises from the fibrous tissues of the mouth, but it is not typically associated with pregnancy and does not regress after delivery.
**Option B:** A mucocele is a benign lesion that arises from the obstruction of a salivary gland duct, but it does not have a specific association with pregnancy and does not typically regress after delivery.
**Option C:** A squamous cell carcinoma is a type of malignant tumor that arises from the squamous epithelium of the mouth, but it is not consistent with the patient's presentation of a benign, self-limiting condition that regresses after delivery.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that pyogenic granulomas can appear in other areas of the body, such as the skin and mucous membranes, and are not exclusive to the oral cavity. They are often associated with minor trauma or irritation, and their appearance can be triggered by hormonal changes, including those that occur during pregnancy.

**Correct Answer:** C. Pyogenic granuloma.