What it measures
Group B streptococcus (GBS), a bacterium that lives in the gut and vagina of many people without causing symptoms. The test looks for it in a swab from the vagina and rectum. The Royal College of Obstetricians and Gynaecologists puts carriage at 2 to 4 in 10 women in the UK.
Why people test it
- Pregnant women who want to know whether they carry GBS, as the NHS does not routinely test for it.
- Checking in a later pregnancy after GBS was found in an earlier one.
Typical range
There is no numeric range. The result is reported as GBS detected or not detected. The report shows how that lab reports it.
Finger-prick or vein?
This is not a blood test. Providers offer it only as a home kit with a swab from the vagina and rectum.
The Royal College of Obstetricians and Gynaecologists describes the ECM (enriched culture medium) swab test as taken at 35 to 37 weeks of pregnancy.