**Core Concept**
Fulminant hepatic failure in pregnancy is most commonly due to **hepatitis E virus (HEV)**, particularly in the third trimester, where it presents with rapid-onset liver dysfunction and coagulopathy. Unlike other hepatitis viruses, HEV has a strong association with pregnancy, especially in endemic areas.

**Why the Correct Answer is Right**
HEV is the most common viral cause of fulminant hepatic failure in pregnancy, especially in the third trimester. It primarily infects hepatocytes and causes direct hepatocyte necrosis, leading to acute liver failure. The virus is transmitted via fecal-oral route and is more severe in pregnant women due to immunological changes and increased liver metabolic demand. HEV infection in pregnancy has a higher risk of progression to fulminant hepatic failure compared to other hepatitis viruses.

**Why Each Wrong Option is Incorrect**
Option A: HAV is not associated with fulminant hepatic failure in pregnancy; it is typically self-limiting and rare in pregnancy.
Option B: HBV can cause chronic infection and liver disease, but fulminant failure is uncommon in pregnancy and usually presents in chronic carriers.
Option C: HCV is associated with chronic hepatitis and cirrhosis, not acute fulminant failure, and is not a leading cause in pregnancy.

**Clinical Pearl / High-Yield Fact**
Pregnant women in endemic areas (e.g., India, China, Southeast Asia) are at high risk for HEV infection, and HEV is the **only** hepatitis virus linked to fulminant hepatic failure in pregnancy. Early recognition and antiviral support are critical.

✓ Correct Answer: D. HEV