A positive swab in a low risk woman

During pregnancy, many women experience symptomatic vaginal discharge, which may prompt health professionals to take a swab for culture.

If GBS is detected during the antenatal period, it is important to explain the following to the woman:

1. GBS is a normal vaginal commensal in up to 30% of the population

2. Antenatal treatment with oral penicillin does not reduce the likelihood of GBS colonisation at the time of delivery, and so is not required

3. A note of the presence of vaginal carriage should be made in the woman’s maternity notes, so health professionals can take appropriate action during labour

4. GBS is highly unlikely to be the cause of the vaginal discharge

The risk of neonatal disease when GBS is detected at 35-37 weeks by swabs taken from the low vagina and rectum and cultured in enrichment medium is around 1 in 500.