The Accuracy of Late Antenatal Screening Cultures in Predicting Intrapartum Group B Streptococcal Colonization
Ekachai Kovavisarach MD*, Porntaj Jarupisarnlert MD*, Suwattana Kanjanaharuetai MSc**
Affiliation : * Department of Obstetrics and Gynecology, Rajavithi Hospital, College of Medicine, Rangsit University, Bangkok ** Department of Pathology, Rajavithi Hospital, Bangkok
Objective : To determine the accuracy of late antenatal (35-37 weeks) screening cultures in predicting intra-
partum 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 betweenPPV and NPV in any interval between antenatal and intrapartum cultures.
Conclusion : Late antenatal screening cultures were not sensitive in predicting intrapartum GBS colonization
status.
Keywords : Group B streptococcus, Antenatal, Intrapartum, Accuracy
