Up to 36% of pregnant women are colonized with Group B Streptococcus (GBS). Preterm delivery in colonized mothers is a risk factor for early onset neonatal GBS disease, but whether maternal GBS genital colonization is related to preterm delivery is unclear. The objective of this review was to determine the relationship between maternal colonization with GBS and preterm delivery. Pubmed searches and reference lists of all selected publications were used to find studies reporting on the relationship between maternal GBS colonization and preterm delivery. Study characteristics were abstracted, and validity scores were performed. To assess the relationship between GBS colonization and pregnancy outcome, four-fold prognostic tables were constructed for each study. Out of more than 60 full-text articles, 16 follow-up studies and four case control studies were included in this review. Follow-up studies were divided into 'cohort studies,' in which cultures were taken early in pregnancy and which reported on pregnancy outcome, and 'cross-sectional studies', in which cultures were collected during delivery. Studies differed widely in methods, validity score, and GBS prevalence. The combined estimate from a random effect meta-analysis of the 11 cohort studies was 1.06 (95% confidence intervals (CI) 0.95-1.19) and for the five cross-sectional studies 1.75 (95% CI 1.43-2.14). For the case control studies, the pooled odds ratio was 1.59 (95% CI 1.03-2.44). This systematic review did not show an association between maternal GBS colonization during pregnancy and preterm delivery. However, in case of preterm delivery, there is an increased risk of subsequent maternal GBS colonization.