**Core Concept**
Fibroids are benign tumors that arise from the smooth muscle layer of the uterus. During pregnancy, fibroids can cause various complications due to their growth and location. The uterus expands significantly during pregnancy, which can lead to an increase in fibroid size and symptoms.

**Why the Correct Answer is Right**
Fibroids are known to cause symptoms such as abdominal pain, pressure, and bladder symptoms during pregnancy. They can also increase the risk of postpartum hemorrhage due to their potential to interfere with placental implantation and uterine contractions. Additionally, large fibroids can lead to preterm labor by causing uterine distension and inflammation. However, metastasis is extremely rare in benign fibroids, as they do not have the ability to invade surrounding tissues or spread to distant sites like malignant tumors do. The lack of metastatic potential is a key characteristic that distinguishes benign fibroids from malignant tumors.

**Why Each Wrong Option is Incorrect**
**Option B:** Pain is a common symptom associated with fibroids during pregnancy, particularly if they are large or pedunculated.
**Option C:** Postpartum hemorrhage is a potential complication of fibroids, especially if they interfere with uterine contractions or placental implantation.
**Option D:** Preterm labor can be caused by fibroids, especially if they are large or multiple, leading to uterine distension and inflammation.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that fibroids can cause significant morbidity during pregnancy, but they do not have the potential for metastasis like malignant tumors do. This distinction is crucial for diagnosis and management.

✓ Correct Answer: A. Metastasis