A 29-year-old woman presents to her obstetrician for her third prenatal clinic visit. She is feeling well, except that she has noted vaginal discharge for the past 4 days. Evaluation includes a vaginal swab sample for nucleic acid amplification testing, which is negative for Chlamydia trachomatis and Neisseria gonorrhoeae, but is positive for Trichomonas vaginalis. Her sex partner is referred for evaluation and presumptive treatment of trichomoniasis.