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Objective:To identify risk factors for group B streptococcus (GBS) colonization in a subsequent pregnancy using microbiological and clinical data from a prior pregnancy.Study Design:A retrospective cohort study of women over a 10-year period, using laboratory records to identify women with GBS culture results available in two successive pregnancies.Result:One thousand eight hundred and ninety-four women met eligibility criteria. Of these, 1293 were not GBS-colonized in either pregnancy, 198 were colonized in both pregnancies and 403 had discordant colonization status. GBS colonization in the index pregnancy was positively associated with multiparity, premature delivery and lower maternal age and negatively associated with chorioamnionitis. The strongest predictor of colonization in a subsequent pregnancy was colonization in the index pregnancy (50% likelihood if colonized compared with 14% if not in the index pregnancy, relative risk 3.6, confidence interval (CI)=3.1 to 4.3). GBS colonization in the subsequent pregnancy was independently associated with: GBS colonization in the index pregnancy (odds ratio (OR)=6.28; CI=4.91 to 8.05), preterm delivery in the index pregnancy (OR=1.80; CI=1.05 to 3.09) and prior early pregnancy loss (OR=1.15; CI=1.04 to 1.27).Conclusion:GBS colonization in a prior pregnancy is informative of colonization in a subsequent pregnancy. These data support providing antimicrobial prophylaxis in unscreened parous women with known prior GBS colonization. [ABSTRACT FROM AUTHOR]