Objective: To determine the risk factors related to group B streptococcal (GBS) colonization in pregnant women on admission in labor.
Material and Method: From the 1st-30 th October 2004, at the Rajavithi Hospital, 320 pregnant women, who fulfilled the specified criteria, were selected for a cross-sectional descriptive study. Swabs were cultured from the lower vagina and anorectum for GBS using Todd-Hewitt broth with nalidixic acid 15 g/ml and gentamicin 8 g/ml only.
Results: Colonization was present in 58 cases (18.12%). The risk factor for GBS colonization was an older mean maternal age and a lower mean gestational age. No mothers or neonates during the study period developed a clinical infection from GBS.
Conclusion: The risk factors for GBS colonization in pregnant women were older maternal age and lower gestational age.

Keywords: Risk factors, Group B streptococcus, GBS, Colonization