(A-300) Risk of Preterm Birth with Clindamycin vs. Metronidazole in Pregnant Women with Bacterial Vaginosis: A Retrospective Cohort Study

Background: Bacterial vaginosis (BV), a common infection during pregnancy, has been associated with an increased risk of adverse pregnancy outcomes, including preterm birth. Metronidazole and clindamycin are the recommended treatments for symptomatic BV in pregnant women, with both demonstrating effectiveness in resolving the infection. However, concerns persist regarding their potential impact on the risk of preterm birth. While some studies suggest differences in preterm birth risk associated with clindamycin and metronidazole, the existing literature is limited, and the findings remain inconsistent.

Objectives: To compare the safety of clindamycin and metronidazole regarding preterm birth risk in pregnant women with BV using real-world data.

Methods: We conducted a retrospective cohort study using Medicaid Analytic eXtract (MAX) data from 1999 to 2014. Pregnant women aged 12–55 years diagnosed with BV during their first pregnancy and initiating either clindamycin or metronidazole within three days of diagnosis were identified. The antibiotic prescription fill date was defined as the index date. To account for baseline differences, 1:3 propensity score (PS) matching was performed based on demographics, selected comorbidities, and other antibiotic use. Conditional logistic regression was employed to compare the risk of preterm birth between clindamycin and metronidazole users, both overall and stratified by the trimester of diagnosis. Subgroup and sensitivity analyses were conducted to assess the robustness of the primary analysis.

Results: We identified 3,569 clindamycin and 8,701 metronidazole users after propensity score matching. The odds of preterm birth did not differ between metronidazole and clindamycin users (adjusted odds ratio [aOR], 1.11; 95% confidence interval [CI], 0.97–1.28). Similarly, no significant difference in preterm birth risk was observed when treatment was initiated in the first (aOR, 1.11; 95% CI, 0.93–1.34), second (aOR, 1.17; 95% CI, 0.89–1.53), or third (aOR, 0.97; 95% CI, 0.76–1.23) trimester. These findings remained consistent across the subgroup and sensitivity analyses.

Conclusions: Our study found no significant difference in the risk of preterm birth between clindamycin and metronidazole in pregnant women with BV. These findings suggest that both antibiotics are equally safe with respect to risk of preterm birth, providing important evidence to guide clinical decision-making in the management of symptomatic BV during pregnancy.