Colonization with Trichomonas vaginalis is a possible cause of poor pregnancy outcome. To facilitate the diagnosis of this condition during pregnancy, we conducted a prospective, multicenter study of 13,816 gravid women who were between 23rd and 26th week of gestation. Findings significantly associated with T. vaginalis colonization included a yellow, green, or bloody discharge from the vagina or cervix; abnormal odor after KOH was added to a vaginal specimen; a vaginal pH of > 5.0; and cervical friability. The amount of vaginal discharge and abnormal consistency of the discharge were also associated with T. vaginalis colonization. These findings (except for cervical bleeding and odor after the addition of KOH to a vaginal specimen, which may be influenced by the presence of other flora) are consistent with those reported elsewhere. The clinical usefulness of these features is minimal, and it is more significant that other microorganisms are makers for trichomoniasis; therefore, controlling for other flora is important in the investigation of T. vaginalis colonization.