Prevalence of maternal group B streptococcus colonization and vertical transmission in low-risk women in a single institute

Background: Intrapartum administration of antibiotics lowers the risk of neonatal group B streptococcus (GBS) infection based on recommended guidelines (a risk-based approach and a culture-based screening approach). However, many pregnant women do not undergo culture-based screening, nor treatment with prophylactic antibiotics after a GBS risk-based approach. Therefore, the value of GBS detection in asymptomatic low-risk pregnant women is controversial. Methods: A cohort study of 354 asymptomatic pregnant women at more than 37 weeks' gestation who were planning to undergo vaginal delivery, and 118 neonates (107 paired samples of both mother and newborn), was conducted to evaluate the GBS colonization rate of these pregnant women and the subsequent vertical transmission rate, using a culture method. Results: The positive rate for GBS culture was 6.2% (22/354). Among 107 paired samples, six maternal samples and one neonatal sample were positive for GBS culture, with an estimated vertical transmission rate of 16.7% (1/6). Conclusion: Although the positive rate of GBS culture was lower in asymptomatic low-risk pregnant women, the possibility of vertical transmission might be high. This finding is worthy of further investigation.