What is gbs test pregnancy

Screening for Group B Streptococcus is a common and routine part of pregnancy.

What is group B streptococcus (GBS)?

GBS is a common bacteria which is often found in the vagina, rectum, or bladder. Women often have GBS without having any symptoms. While the bacteria may not cause any problems for the mother, if it infects the baby it can cause rare but serious complications. Around 15-40% of all pregnant women are GBS positive. About 40-70% of those will pass the bacteria to their babies during the birth process, but only 1 in 2000 babies will develop an infection. It is recommended that all women be screened for the bacteria during pregnancy.

What does the screening test involve?

You will usually be screened for GBS between 35 and 37 weeks of gestation. The test is easy and painless, and is conducted by swabbing the vagina and rectum with a cotton-tipped swab. You have the option of doing the swabbing yourself. The swab is then cultured to see if GBS is present. Even if you have a planned Caesarean delivery, you will still need to be screened for GBS in case your water breaks or you go into labour before the scheduled delivery.

What are the risk factors for transmission of GBS to my baby?

Certain factors make it more likely that your baby will become infected with GBS, if you test positive for GBS. These include:

• Starting labour or rupture of membranes before 37 weeks gestation
• Your membranes rupture during labour at full term, and the labour it is likely to last more than 18 hours
• You have an unexplained, mild fever during labour
• You have previously had a baby with a GBS infection
• You have had GBS detected in your urine or have had a bladder infection caused by GBS

What if I test positive for GBS?

If you test positive for GBS or have any of the above conditions, you will be treated with intravenous antibiotics when you go into labour, or if your water breaks early. Although it is rare, your baby will still be monitored closely for symptoms of an infection. An infection may show up in the first 7 days, or after that. The early-onset type of infection can be very serious, and this is why GBS-positive women are treated during labour. If your baby shows signs of GBS infection, he or she will be treated with antibiotics.

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

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.

If you have any questions about Group B Strep, please call our helpline

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Group B strep is a type of bacteria called streptococcal bacteria.

It's very common in both men and women and usually lives in the bottom (rectum) or vagina. It affects 2 to 4 women in 10.

Group B strep is normally harmless and most people will not realise they have it.

It's usually only a problem if it affects:

• pregnant women – it could spread to the baby
• young babies – it can make them very ill
• elderly people or those who are already very ill – it can cause repeated or serious infections

This page focuses on group B strep in pregnancy and babies.

Group B strep is common in pregnant women and rarely causes any problems.

It's not routinely tested for, but may be found during tests carried out for another reason, such as a urine test or vaginal swab.

Risks in pregnancy

If you have group B strep while you're pregnant:

• your baby will usually be healthy
• there's a small risk it could spread to your baby during labour and make them ill – this happens in about 1 in 1,750 pregnancies
• there's an extremely small risk you could miscarry or lose your baby

What to do if you're worried

If you're worried about group B strep, speak to your midwife or GP for advice.

Talk to them about the risks to your baby and ask their advice about whether to get tested.

Routine testing is not currently recommended and tests are rarely done on the NHS, but you can pay for one privately.

Find out more about getting tested for group B strep on the Group B Strep Support website

What happens if you have group B strep

If tests find group B strep, or you've had a baby that's been affected by it before, you may need extra care and treatment.

You may be advised to:

• speak to your midwife about your birth plan – they may recommend giving birth in hospital
• contact your midwife as soon as you go into labour or your waters break
• have antibiotics into a vein during labour – this can significantly reduce the risk of your baby getting ill
• stay in hospital for at least 12 hours after giving birth so your baby can be monitored – this is not always necessary

If you had group B strep during pregnancy, there's a small risk it could spread to your baby and make them very ill.

If this happens, it's usually soon after they're born. Your baby may be monitored in hospital for up to 12 hours to check for any problems.

They'll be given antibiotics into a vein if they develop symptoms.

What to look for after leaving hospital

Occasionally, symptoms of a group B strep infection can develop up to 3 months after birth.

Call 999 or go to A&E if your baby gets any of these symptoms:

• being floppy or unresponsive
• grunting when breathing, or working hard to breathe when you look at their chest or stomach
• very fast or slow breathing
• an unusually high or low temperature
• changes in their skin colour or blotchy skin
• not feeding well or vomiting milk up
• an unusually fast or slow heart rate

They may need treatment with antibiotics in hospital immediately.

Risks in babies

Most babies with a group B strep infection make a full recovery if treated.

Some babies may develop serious problems like sepsis or meningitis.

This can cause lasting problems like hearing loss or loss of vision. Sometimes it can be fatal.

Page last reviewed: 12 March 2021
Next review due: 12 March 2024