Why and when should I test for group B Strep?

Why should I order a group B Strep test?

Carrying group B Strep has no symptoms, so testing is the only way to find out if you are carrying the bacteria.

A group B Strep test is simple, safe and effective.

If a women is known to carry group B Strep in her current pregnancy then she will be offered antibiotics from onset of labour which will minimise the risk of her newborn baby developing a group B Strep infection. Group B Strep is the most common cause of infection in newborn babies causing meningitis, sepsis and pneumonia.

At present, not every pregnant woman in the UK is offered testing for GBS on the NHS. If you are offered a test on the NHS it’s very important to find out which test they’re using (click here for more information on the different types of tests) as not all tests are equally reliable. If you are unable to be tested on the NHS using the GBS-specific Enriched Culture Medium (ECM) test, you can opt to pay for this privately (click here for information about private ECM tests).

Do I need to test for group B Strep in each pregnancy?

If group B Strep was detected in a previous pregnancy and your baby did not develop a group B Strep infection, there is a 1 in 2 (50%) chance that you will be carrying group B Strep again in your next pregnancy.

To help you choose whether you would like to have IV antibiotics in labour, you can have a specific swab test (known as the Enriched Culture Medium or ECM test) to see whether you are carrying GBS when you are 35-37 weeks pregnant.

Clinical guidelines recommend that you should be offered this ECM test for free by the NHS, but we have had feedback that not all NHS hospitals yet offer this. If your hospital is unable to offer ECM testing, you can choose to purchase a test privately

When should I do a group B Strep test?

If you would like to be tested for GBS, talk with your midwife so you can discuss the options available on the NHS first. If you decide to order the test privately, most women would aim to test within the last 5 weeks before they are due to give birth (between 35-37 weeks’ of pregnancy).

You can test earlier in pregnancy, but the test result is not as reliable at predicting what your carriage status will be (positive or negative) when you give birth. The test can also be done later, but the chance increases that the baby will arrive before the test result does.

If you have a history of going into labour early or are expecting twins (or more), you may want to take this into account when doing your group B Strep test.

So why aren’t all women tested for GBS during pregnancy in the UK?

The UK National Screening Committee does not recommend testing all pregnant women for GBS carriage because:

• many women carry the GBS bacteria and, in the majority of cases, their babies are born safely and do not develop an infection.
• screening all women late in pregnancy cannot accurately predict which babies will develop GBS infection.
• no screening test is entirely accurate: a negative swab test does not guarantee that you will not be carrying GBS when you give birth.
• many babies who are severely affected by GBS infection are born preterm, before the suggested time for testing (35-37 weeks)
• giving antibiotics to all women who carry GBS would mean that a very large number of women would receive treatment they do not need.

Related pages

Where to order a group B Strep test

Different types of group B Strep tests

Group B Strep and pregnancy