Number of colony forming units in urine at 35–37 weeks’ gestation as predictor of the vaginal load of Group B Streptococci at birth

Abstract Objective To evaluate GBS colony numbers in the urine at 35–37 weeks’ gestationto predict the load of GBS-colonization of the vagina at birth. Study design In this prospective observational study, we included 902 unselected pregnant women. Exposure was GBS colony forming units(CFU) per mL urine at 35–37 weeks’ gestation. Outcome was vaginalGBS colonization at birth as assessed by a semi-quantitative culture of a vaginalswab sample (negative, +1, +2, +3). Results Bacteriuriawith GBS at 35–37 weeks’ gestationperformed with a sensitivity of 30% concerning any degree of vaginalGBS colonization at birth (31 of 104 cases); 19% for light (+1), 17% for medium (+2), and 52% for high load (+3) vaginalGBS colonization. The colony count in case of GBS bacteriuriaat 35–37 weeks’ gestationperformed with positive predictive values of 35% for 4  CFU/mL, 70% for 10 4 CFU/mL, and 67% for >10 4  CFU/mL. Conclusion Even though the urinary GBS CFU at 35–37 weeks’ gestationis strongly associated with a high load of vaginalGBS colonization intrapartum, it may not perform satisfactorily as a standalone-screening marker for risk of early-onset GBS disease.