Why test for GBS?

With infections as serious as those caused by GBS, prevention is so much better than treatment.

Currently the best way of knowing which women carry GBS in labour is through testing for GBS at 35-37 weeks of pregnancy – using sensitive enriched culture method (ECM) tests. If positive, then preventative measures can minimise the risk of transmission to the bay. Intravenous antibiotics given in labour to women whose babies are at higher risk of developing GBS infection have proved to dramatically reduce that risk.

Screening for GBS is not recommended by the UK National Screening Committee nor the Royal College of Obstetricians & Gynaecologists. Current policy is centred around using a ‘risk factor’ approach to determining which women are at-risk. Unfortunately, the introduction of this strategy in 2003 has not reduced the rate of early-onset GBS infections in babies. Furthermore, up to 40% of babies who do become affected are born to mothers with no clinical risk factors, other unknowingly carrying GBS.

An antenatal screening program, using tests specifically designed to detect group B Strep carriage, would identify more women whose babies are at increased risk of GBS infection than using risk factors. Giving all higher-risk women targeted, low-spectrum antibiotics in labour could result in a significant drop in the cases of early onset GBS infection. Countries that have done this have seen their incidence fall by 71-86%. Research found that, as a result of these additional cases being prevented, this could save the government an estimated £37 million per year.

Without testing low-risk women for GBS carriage, many pregnant women whose babies are at raised risk of GBS infection simply won’t be identified and so no preventative medicine can be given.

Laboratory testing is the only way in which GBS carriage can be reliably identified.

Knowing the result of a test sensitive for GBS test is always good news. If it’s negative within 5 weeks of delivery, then it’s hugely unlikely the baby will develop GBS infection. If it’s positive, although it does mean that the baby is at a raised risk of developing GBS infection, it also means the risk is known so simple, straightforward steps can be taken which have been proven to be extremely effective at minimising that risk.