Evaluation of Antimicrobial Prophylaxis to Prevent Syphilis in Pregnancy in Patients at Risk in Rio de Janeiro, Brazil

The goal of this clinical trial is to learn if benzathine penicillin works to prevent maternal syphilis. It will also learn about the safety of benzathine penicillin. The main questions it aims to answer are: * Does benzathine penicillin lower the rate of syphilis in pregnancy? * What medical problems do participants have when taking benzathine penicillin? Researchers will compare benzathine penicillin to routine care to see if benzathine penicillin works to prevent syphilis. Participants will: * Take benzathine penicillin or receive routine care during the third trimester of pregnancy * Visit the clinic once a month for injections and tests * Report any reactions to benzathine penicillin to the study team