**Core Concept**
Hepatitis B is a viral infection that affects the liver, and it can be transmitted from mother to child during pregnancy, particularly if the mother is a chronic carrier.

**Why the Correct Answer is Right**
Hepatitis B is prevalent in pregnancy due to the high risk of vertical transmission, which occurs when the virus is passed from mother to child during delivery. This can lead to acute hepatitis B infection in the newborn, which may progress to chronic hepatitis B infection. The risk of transmission is higher if the mother is a chronic carrier of the virus, particularly if she is hepatitis B e-antigen (HBeAg) positive. The hepatitis B surface antigen (HBsAg) is used to diagnose chronic hepatitis B infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because hepatitis C is another viral infection that affects the liver, but it is less commonly transmitted from mother to child during pregnancy compared to hepatitis B.
**Option B:** This option is incorrect because hepatitis A is a self-limiting infection that is usually transmitted through the fecal-oral route, and it is not typically associated with vertical transmission during pregnancy.
**Option C:** This option is incorrect because hepatitis D is a rare form of hepatitis that can only infect individuals who are already infected with hepatitis B.

**Clinical Pearl / High-Yield Fact**
It is essential for pregnant women to be screened for hepatitis B infection to identify those who are chronic carriers and at risk of transmitting the virus to their newborns.

**Correct Answer: B. Hepatitis A.**