If a test finds you are carrying GBS, this is perfectly natural and normal – you just may wish to have precautionary IV antibiotics during labour and delivery.

Any test result positive for GBS during pregnancy means that the pregnant woman should be offered intravenous antibiotics from the start of labour or waters breaking and then usually 4-hourly until delivery. Your health professionals should discuss this with you.

The reliability of a negative GBS test result varies depending upon which test it is:

High Vaginal Swab (HVS)

Whilst a positive HVS result is highly reliable, a negative one is not. Only around 50% of women who are carrying GBS when the swabs are taken will correctly be told they carry GBS – the other half will be incorrectly told they don’t. So trust a positive HVS result, but be wary of a negative one!

This test is recognised as optimal for detecting GBS carriage by both the Royal College of Obstetricians & Gynaecologists and by the Health Protection Agency, it is not available routinely on the NHS. This test is highly sensitive and has been specifically designed for the isolation of GBS.

Research shows that, if the ECM test is performed within 5 weeks of delivery, a negative result is 96% predictive of not carrying GBS at delivery (so in that trial 4% of women acquired carriage between the test and giving birth) and a positive result is 87% predictive of carrying GBS at delivery (so 13% of women lost carriage between performing the test and giving birth).

A negative ECM test result means that the pregnant woman would not need to be offered intravenous antibiotics from the onset of labour or waters breaking against GBS infection in her baby.

Where no ECM test result is available OR the less reliable NHS test has come back negative, then the pregnant woman should be offered intravenous antibiotics during labour against GBS infection in her baby if one or more risk factors is present (click here for more information on risk factors).