Intrapartum tests for group B streptococcus: accuracy and acceptability of screening


J Daniels, University of Birmingham, Reproduction, Genes and Development, Birmingham Women’s Hospital, Metchley Park Road, Edgbaston, Birmingham, B15 2TG, UK. Email


Please cite this paper as: Daniels J, Gray J, Pattison H, Gray R, Hills R, Khan K on behalf of the GBS Collaborative Group. Intrapartum tests for group B streptococcus: accuracy and acceptability of screening. BJOG 2011;118:257–265.

Objective  To assess the accuracy and acceptability of polymerase chain reaction (PCR) and optical immunoassay (OIA) tests for the detection of maternal group B streptococcus (GBS) colonisation during labour, comparing their performance with the current UK policy of risk factor-based screening.

Design  Diagnostic test accuracy study.

Setting and population  Fourteen hundred women in labour at two large UK maternity units provided vaginal and rectal swabs for testing.

Methods  The PCR and OIA index tests were compared with the reference standard of selective enriched culture, assessed blind to index tests. Factors influencing neonatal GBS colonisation were assessed using multiple logistic regression, adjusting for antibiotic use. The acceptability of testing to participants was evaluated through a structured questionnaire administered after delivery.

Main outcome measures  The sensitivity and specificity of PCR, OIA and risk factor-based screening.

Results  Maternal GBS colonisation was 21% (19–24%) by combined vaginal and rectal swab enriched culture. PCR test of either vaginal or rectal swabs was more sensitive (84% [79–88%] versus 72% [65–77%]) and specific (87% [85–89%] versus 57% [53–60%]) than OIA (P < 0.001), and far more sensitive (84 versus 30% [25–35%]) and specific (87 versus 80% [77–82%]) than risk factor-based screening (P < 0.001). Maternal antibiotics (odds ratio, 0.22 [0.07–0.62]; P = 0.004) and a positive PCR test (odds ratio, 29.4 [15.8–54.8]; P < 0.001) were strongly related to neonatal GBS colonisation, whereas risk factors were not (odds ratio, 1.44 [0.80–2.62]; P = 0.2).

Conclusion  Intrapartum PCR screening is a more accurate predictor of maternal and neonatal GBS colonisation than is OIA or risk factor-based screening, and is acceptable to women.