Group B strep in pregnancy: testing and what happens in labour

Group B strep is a common bacterium that is usually harmless but can, rarely, make newborn babies seriously ill. Here’s what it is, whether you’ll be tested, and what happens if you have it.

What is group B strep (GBS)?

Tommy’s says GBS is a common bacterium that lives in the gut, vagina and rectum. It’s normally harmless, and many people carry it without knowing. It can pass to a baby during labour. Tommy’s says about 1 in 1,750 newborns in the UK and Ireland is diagnosed with early-onset GBS infection (within 6 days of birth).

Will I be tested?

Tommy’s says GBS is not routinely tested for in the UK. The reasons given are that GBS is very common, the tests aren’t fully accurate and infection can’t be predicted. There are some exceptions:

If you had GBS in a previous pregnancy, Tommy’s says you’ll be offered a swab test at 35 to 37 weeks.
If a urine test or swab in this pregnancy finds GBS, you’ll be offered antibiotics in labour.

Testing privately

You can pay for a test. The charity Group B Strep Support recommends the Enriched Culture Medium (ECM) test, using a swab from low in the vagina and from the rectum. It says kits cost from around £38, and results come within about 3 working days of the lab receiving your swabs. Most people aim to test in the last 5 weeks before the due date. Antibiotics can affect results, so the charity advises leaving 7 to 10 days between finishing antibiotics and testing. It says standard NHS swabs are less reliable and can miss up to half of women who carry GBS at delivery, and some NHS trusts offer ECM to some or all pregnant women. The charity lists availability at gbss.org.uk/test.

If cost is a barrier, Tommy’s suggests talking to your doctor or midwife.

If GBS is found

Tell your midwife, and discuss where to give birth. Tommy’s says you should be offered antibiotics through a drip (IV) in labour. Group B Strep Support says this should start as soon as possible once labour starts or your waters break, and that a first dose 4 or more hours before birth is highly effective. Tablets are not recommended for preventing GBS in pregnancy or labour. After the birth, your baby may be monitored for a time, depending on when you had antibiotics. GBS found in a swab usually does not need treatment before labour starts, as oral antibiotics are not recommended to clear carriage (Group B Strep Support). If GBS is found in a urine sample, your midwife will explain whether treatment is needed.

Support

Group B Strep Support’s helpline is 0330 120 0796. Tommy’s midwives are on 0800 0147 800, 9am to 5pm Monday to Friday. For signs that labour is starting, see signs of labour.

If you’re worried about your baby after the birth, tell your midwife or get urgent medical help.

Questions people ask

Does having GBS change how my baby is born?

It can affect your plans in some situations. For example, the NHS says that if your waters have broken and you’re between 34 and 37 weeks and GBS is found, immediate induction or a caesarean may be offered. Talk through your plan with your midwife.

Can I get rid of GBS before labour?

Group B Strep Support says oral antibiotics are not recommended to prevent GBS carriage in pregnancy or labour.

Where does GBS come from?

Tommy’s says it is a common bacterium that lives in the gut, vagina and rectum, and it is normally harmless.

Will I be offered antibiotics if my waters break early?

If you’re under 37 weeks and your waters have broken, call your maternity unit straight away. The NHS says you’ll be offered antibiotics and tests for infection.