The accuracy of late antenatal screening cultures in predicting intrapartum group B streptococcal colonization.

Objective: To determine the accuracy of late antenatal (35-37 weeks) screening cultures in predicting intrapartum group B streptococcal (GBS) colonization in Rajavithi Hospital (RH).

Material And Method: From the September 1st, 2006 to November 30th, 2006 at RH, 360 pregnant women who fulfilled the specified criteria were selected from antenatal clinic. Swabs were cultured from the lower vagina and anorectum for GBS using Todd-Hewitt broth with 15 mcg/ml nalidixic acid and 8 mcg/ml gentamicin. When they were admitted in the labor room (LR) for labor; the cultures were repeated in the same way.

Results: 302 out of 360 cases had been cultured in LR. The prevalence of GBS in pregnant women at 35-37 weeks and delivery were 13.05% and 13.58% respectively. Fifty-three out of 302 cases were colonized with GBS from at least ANC and/or LR. So the overall prevalence of GBS colonization in pregnant women in this study was 17.55% (53/302). The sensitivity, specificity, positive and negative predictive values of late antenatal GBS culture were 70.73%, 95.40%, 70.73% and 95.40% respectively. There was no significant difference between PPV and NPV in any interval between antenatal and intrapartum cultures.

Conclusion: Late antenatal screening cultures were not sensitive in predicting intrapartum GBS colonization status.