**Core Concept**
Mifepristone is an antiprogestin medication that works by blocking the action of progesterone, a hormone essential for maintaining pregnancy. It is used in various medical conditions, including abortion, fibroids, and certain types of cancer. However, its use is contraindicated in certain situations due to its mechanism of action.

**Why the Correct Answer is Right**
Mifepristone is not used in threatened abortion because the pregnancy is still viable, and the goal of treatment is to maintain the pregnancy. Mifepristone's action as an antiprogestin would actually induce abortion, making it counterproductive in this scenario. In contrast, mifepristone is effective in inducing labor in cases of ectopic pregnancy and molar pregnancy, where the pregnancy is no longer viable. In the case of fibroids, mifepristone can help shrink the tumor by blocking the action of progesterone, which is essential for the growth of fibroids.

**Why Each Wrong Option is Incorrect**
**Option B:** Fibroids are a common indication for the use of mifepristone, as it can help shrink the tumor by blocking the action of progesterone.
**Option C:** Ectopic pregnancy is a condition where the pregnancy is no longer viable, and mifepristone can be used to induce labor and resolve the pregnancy.
**Option D:** Molar pregnancy is another condition where mifepristone can be used to induce labor and resolve the pregnancy.

**Clinical Pearl / High-Yield Fact**
Mifepristone is a key medication in the management of ectopic pregnancy and fibroids, but its use is contraindicated in threatened abortion due to its action as an antiprogestin. It is essential to understand the mechanism of action of mifepristone and its indications to avoid using it inappropriately.

**Correct Answer:**
✓ Correct Answer: A. Threatened aboion