**Core Concept**
Intrahepatic cholestasis of pregnancy (ICP) is a condition characterized by impaired bile flow, leading to elevated bile acids in the bloodstream. This condition poses a significant risk to both the mother and the fetus, necessitating prompt and effective treatment.

**Why the Correct Answer is Right**
The treatment of choice for ICP is ursodeoxycholic acid (UDCA), a bile acid that helps to reduce bile acid levels in the blood and alleviate symptoms. UDCA works by increasing the excretion of bile acids into the bile, thereby reducing the amount of bile acids in the bloodstream. This helps to decrease the risk of complications associated with ICP, such as preterm labor and fetal distress.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because corticosteroids, such as betamethasone, are used to accelerate fetal lung maturity in cases of preterm labor, not to treat ICP.

**Option B:** This option is incorrect because vitamin K is used to prevent bleeding in newborns, particularly those with risk factors for bleeding such as prematurity or low birth weight, not to treat ICP.

**Option C:** This option is incorrect because antihistamines, such as ranitidine, are used to treat conditions such as gastroesophageal reflux disease (GERD) and peptic ulcer disease, not ICP.

**Clinical Pearl / High-Yield Fact**
It's essential to note that UDCA is the only FDA-approved treatment for ICP, and its use should be initiated promptly after diagnosis to minimize the risk of complications.

**Correct Answer: C. Ursodeoxycholic acid (UDCA).**