When the pregnant women is admitted due to first stage of labor , the investigator will inform the patients. If the patients give consent, the patient's data will be collect in case record form. the patients will be swab at posterior fornix and around anus to collect specimen and send to microbiology lab before per vaginal examination. After the patients finish in labor, perineal wound will be swab to collect specimen and send to microbiology lab. Then the patients are randomized in two group, the first one will receive amoxicillin and the second one will receive placebo. During admission the patients will be exam by investigator every day. After the patients are discharge, the follow up will be appoint on 6 weeks later. The infant will be swab at rectum to collect specimen and send to microbiology lab when the patient's discharge day. Every specimen will be culture for bacteria and perform antimicrobial susceptibility test for amoxicillin.