Background STIs among pregnant women contribute maternal and infant morbidity. There are limited data on STIs among pregnant adolescents. We determined and compared prevalence and correlates of STIs among pregnant adolescent and adult women in Western Kenya.

Methods HIV-1 negative women were enrolled during pregnancy. Demographic and clinical characteristics and blood and genital samples were collected. Chlamydia trachomatis (CT) and Neisseria gonorrhoea (GC) were detected using endocervical nucleic acid amplification, syphilis by rapid plasma reagin tests, and trichomonas vaginalis (TV) by wet preparations. Analyses were restricted to adolescents (age 14–21) and adults (age > 21) with STI data.

Results Among 1156 HIV-1 negative pregnant women, median age was 22 years and 537 (46%) were adolescents. Adolescents were less likely to be married (64% vs. 92%; p < 0.001) and more likely to have traded sex (13% vs. 3%; p = 0.05); adolescents and adults had similar prevalence of prior STIs (7%), vaginal drying (18%) and unprotected sex during past month (56%). The prevalence of STIs was: CT, 5%; GC, 2%; TV, 6%; and syphilis 1%. Compared to adults, risk of CT (odds ratio (OR) = 3.23; 95% Confidence interval (CI) = 1.83–7.73), GC (OR = 1.87, 95% CI = 0.84–4.16), and TV (OR = 1.61, 95% CI = 1.00–2.60) were higher among adolescents, but syphilis risk was lower (OR = 0.25, 95% CI = 0.05–1.17). Among adolescents, CT risk factors included ever trading sex (aOR = 2.71, 95% CI = 1.06–13.33). Among adults, TV risk factors included vaginal drying and lifetime number of sex partners; CT risk factors included vaginal drying and younger age. History of STI was a risk factor for syphilis among both adolescents and adults. No risk factors were identified for gonorrhoea.

Conclusion Prevalences of CT, GC, and TV were significantly higher among adolescents than adults in this pregnant cohort. Trading sex was more prevalent in adolescents and was associated with a 2.7-fold increased risk for CT among adolescents. Tailoring pregnancy STI screening approaches for adolescents may be useful.