You are answering a USMLE-style medical question. Question: A previously healthy 29-year-old woman, gravida 1, para 0, at 35 weeks' gestation comes to the physician for a routine prenatal visit. Current medications include folic acid and a multivitamin. A rectovaginal swab culture grows bacitracin-resistant colonies of gram-positive cocci with surrounding areas of clear hemolysis. Which of the following is the most appropriate intervention to decrease vertical transmission of this organism? Options: A) Abstain from breastfeeding B) Administer ampicillin intrapartum C) Perform amniocentesis at 37 weeks D) Administer intravenous immune globulin postpartum Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.