Final answer:
Hepatitis E (HEV) poses the greatest risk of substantial morbidity and mortality during pregnancy, with mortality rates as high as 20-25% in pregnant women in the third trimester.
Step-by-step explanation:
The form of hepatitis with the greatest risk of substantial morbidity and mortality during pregnancy is Hepatitis E (HEV). Hepatitis E, particularly in pregnant women, has been associated with severe outcomes and a high case fatality rate, much more so than the other hepatitis viruses.
Hepatitis E is transmitted through the consumption of contaminated water or food and has a high rate of fulminant hepatitis, which can lead to liver failure in pregnant women. Mortality rates can be as high as 20-25% in pregnant women in the third trimester, which is substantially higher than those associated with the other forms of viral hepatitis. Although it is less commonly seen in developed countries, HEV is a significant concern in areas with poor sanitation.