What is the first-line antibiotic for maternal GBS prophylaxis during labor?

• A. Tetracycline
• B. Penicillin G
• C. Erythromycin
• D. Vancomycin

Answer: (B)

Penicillin G is used for intrapartum GBS prophylaxis because it is highly effective against group B Streptococcus and safe for both mother and baby. When administered during labor, it significantly reduces the risk of early-onset GBS disease in newborns. Its narrow spectrum minimizes disruption to other bacteria and lowers the chance of resistance developing, making it the preferred first-line choice.

Tetracycline is avoided in pregnancy due to potential effects on fetal bones and teeth. Erythromycin is less reliable today because many GBS strains are resistant to macrolides. Vancomycin is reserved for cases where a beta-lactam antibiotic cannot be used (such as a severe penicillin allergy or proven beta-lactam–resistant GBS), not the first-line choice.