• We used Bayes' theorem to evaluate the probability of vaginal foreign bodies in girls with genital complaints. The prevalence of vaginal foreign bodies in outpatient girls under 13 years of age with gynecologic disorders was found to be 4%. Review of the charts of 17 pre-menarcheal girls who had foreign bodies on 19 occasions and of 28 girls with infectious or nonspecific vaginitis demonstrated that patients with foreign bodies reported vaginal bleeding more frequently than discharge (14 and two of 15 symptomatic cases, respectively), while in contrast, patients with infectious or nonspecific vaginitis reported vaginal discharge more often than bleeding (23 and five of 28 symptomatic controls, respectively). Bayes' theorem indicates that, in populations resembling the one we studied, approximately 18% of preteenage girls with vaginal bleeding with or without discharge and 50% of those with bleeding and no discharge will prove to have vaginal foreign bodies.
Paradise JE, Willis ED. Probability of Vaginal Foreign Body in Girls With Genital Complaints. Am J Dis Child. 1985;139(5):472-476. doi:10.1001/archpedi.1985.02140070046031