Vaginal progesterone is associated with decreased group B streptococcus colonisation at term: a retrospective cohort study

Objective To investigate whether women using intravaginal progesterone suppositories for preterm birth prevention during pregnancy will have lower rates of group B streptococcus (GBS) colonisation at term, compared with women receiving intramuscular 17-alpha-hydroxyprogesterone caproate. Design This was a retrospective observational cohort study of women who were prescribed a progestogen during their pregnancy for preterm birth prevention, and who delivered at term. Setting A tertiary referral hospital in central Ohio. Population Patients who were prescribed a progestogen during their pregnancy for preterm birth prevention between 2004 and 2017 were included in the study. Patients who delivered at <37 weeks of pregnancy, switched progestogen type during the pregnancy, or had a pessary or cerclage placed were excluded. Methods Baseline characteristics were compared using Mann-Whitney U-test or Chi-square test as appropriate. The association between type of progestogen and GBS colonisation was assessed using bivariate and multivariable analyses. Main outcome measures The primary outcome was GBS colonisation. Results In all, 565 patients were included in the study, of whom 173 received intravaginal progesterone, and 392 17-alpha-hydroxyprogesterone caproate. Patients receiving intravaginal progesterone were less likely to be colonised with GBS (19.7 versus 28.1%). After adjustments for potential confounders were made in a multivariable logistic regression analysis, receiving intravaginal progesterone suppositories (adjusted odds ratio [OR] 0.61, 95% CI 0.39-0.95) was associated with reduced GBS colonisation. Conclusions Intravaginal progesterone is associated with a decreased prevalence of rectovaginal GBS colonisation at term. Tweetable abstract Vaginal progesterone is associated with a lower incidence of rectovaginal GBS colonisation, compared with 17 alpha-hydroxyprogesterone caproate.