**Core Concept**
Meningococcal meningitis is a severe infection caused by the bacterium Neisseria meningitidis, which can lead to sepsis and death if left untreated. Pregnant women are at increased risk of severe disease due to immunosuppression. Prophylactic antibiotics are essential to prevent disease transmission among close contacts.

**Why the Correct Answer is Right**
Rifampicin is the recommended prophylactic antibiotic for meningococcal meningitis in pregnant women. It is a bactericidal antibiotic that inhibits RNA synthesis by binding to the beta-subunit of RNA polymerase. Rifampicin achieves high concentrations in the cerebrospinal fluid and is effective against Neisseria meningitidis. It is generally considered safe for use in pregnancy, although it can cause transient changes in liver function tests.

**Why Each Wrong Option is Incorrect**
**Option A:** Ciprofloxacin is not recommended for prophylaxis of meningococcal meningitis in pregnant women due to the potential risk of cartilage damage to the developing fetus.
**Option B:** Co-trimoxazole is not the preferred choice for meningococcal meningitis prophylaxis in pregnancy, as rifampicin is more effective and has a better safety profile.
**Option C:** Doxycycline is contraindicated in pregnancy due to the risk of inhibiting bone growth and causing tooth discoloration in the fetus.

**Clinical Pearl / High-Yield Fact**
Rifampicin is also used to treat latent Mycobacterium tuberculosis infection, and its use can lead to a false-positive result on the urinary antigen test for Legionnaires' disease.

**Correct Answer:** B. Rifampicin.