STUDY OBJECTIVE:To examine the prevalence, symptomatology, risk factors, and other infections associated with urogenital chlamydial infection in pregnant teenagers. DESIGN:Retrospective case-control study by medical record review. SETTING:Prenatal care clinic for adolescents at University of Tennessee Medical Center, Knoxville, Tennessee. PARTICIPANTS:Pregnant adolescents younger than 19 years of age who were diagnosed with chlamydial infection on the first prenatal visit from 1988 to 1994 were studied. Pregnant adolescents of similar age and socioeconomic background who came in the same day for the first prenatal visit, but were not infected, made up the control group. INTERVENTION:Routine prenatal questionnaires regarding personal and medical histories, and routine prenatal screening, including pelvic examination with Papanicolaou (PAP) smear and laboratory investigations for common genital infections and sexual transmitted disease (STDs), were obtained. MAIN OUTCOME MEASURES:Analyzed the prevalence of chlamydial infection and compared the infected group to the control group with regard to race, behavioral factors, symptoms, prenatal screening results, other concurrent genital infections, and histories of STDs. RESULTS:Of a total population of 596 pregnant teenagers, 67 (11.24%) were infected with Chlamydia trachomatis. In multivariate analysis, black race (odds ratio [OR] = 4.01; 95% confidence interval [CI] = 1.74-9.23; p = 0.001) and greater gestational age at first prenatal visit (OR = 1.11; 95% CI = 1.04-1.18; p = 0.001) were independently associated with chlamydial infection. Age, marital status, number of pregnancies, smoking, alcohol abuse, drug abuse, age at first intercourse, and multiple sex partners were not associated with the infection. Likewise, the symptom of vaginal discharge (a complaint of > 70% in each group), other genital co-infections (found > 50% in each group, mainly candidiasis and bacterial vaginosis), abnormal PAP smears (found > 60% in each group) and histories of STDs or previous chlamydial infection were not significantly different between case and control groups. Human papillomavirus infection, trichomonal infection, and dysplasia or atypia were found more often in patients infected with chlamydia, but were not statistically significant. CONCLUSION:Pregnant adolescents in east Tennessee were at risk for chlamydial infection as well as for other genital infections and abnormal PAP smears. Routine prenatal chlamydial screening is warranted because of a lack of specific symptoms.