**Core Concept**
Fulminant hepatitis in pregnancy is a life-threatening condition characterized by rapid onset of liver failure, often resulting in coagulopathy and encephalopathy. The most common causes of fulminant hepatitis in pregnant women are viral infections, with hepatitis E virus (HEV) being a leading cause in developing countries.

**Why the Correct Answer is Right**
Hepatitis E virus (HEV) is a major cause of fulminant hepatitis in pregnant women, particularly in developing countries. HEV infection is transmitted through the fecal-oral route, and the virus replicates in the liver, leading to liver injury and failure. The pathogenesis of HEV involves the virus's ability to infect hepatocytes and induce a strong inflammatory response, resulting in liver damage and failure. In pregnant women, especially in the third trimester, the risk of HEV infection is higher due to changes in the immune system and increased susceptibility to the virus.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatitis B virus (HBV) is also a cause of fulminant hepatitis, but it is less common in pregnant women compared to HEV. HBV infection is transmitted through bodily fluids, and the virus can cause liver damage and failure, but it is not the most common cause in pregnancy.
**Option B:** Autoimmune hepatitis is a rare cause of fulminant hepatitis in pregnant women. It is characterized by an abnormal immune response against liver cells, leading to inflammation and damage. However, it is not the most common cause of fulminant hepatitis in pregnancy.
**Option C:** Acetaminophen overdose is a common cause of fulminant hepatitis, but it is not the most common cause in pregnant women. Acetaminophen toxicity can cause liver damage and failure, but it is often preventable with proper medication use and monitoring.
**Option D:** Viral hepatitis C is a chronic infection that can cause liver damage and failure, but it is not typically associated with fulminant hepatitis in pregnancy.

**Clinical Pearl / High-Yield Fact**
In pregnant women, especially in developing countries, hepatitis E virus (HEV) is a leading cause of fulminant hepatitis. It is essential to consider HEV infection in the differential diagnosis of fulminant hepatitis in pregnant women, particularly in areas where the virus is endemic.

**Correct Answer: C. Hepatitis B virus (HBV) is also a cause of fulminant hepatitis, but it is less common in pregnant women compared to HEV.**