What is a group b strep test in pregnancy

Rates of serious group B strep (GBS) infections are higher among newborns, but anyone can get GBS disease. Below are some important facts about GBS disease in babies, pregnant women, and others.

Babies

• Among babies, there are 2 main types of GBS disease:

• • Early-onset — occurs during the first week of life.
  • Late-onset — occurs from the first week through three months of life.

• In the United States, GBS bacteria are a leading cause of meningitis and bloodstream infections in a newborn’s first three months of life.

• Early-onset disease used to be the most common type of GBS disease in babies. Today, because of effective early-onset disease prevention, early- and late-onset disease occur at similarly low rates.
• In the United States on average each year:
  • About 930 babies get early-onset GBS disease.
  • About 1,050 babies get late-onset GBS disease.
• Newborns are at increased risk for GBS disease if their mother tests positive for the bacteria during pregnancy.
• 2 to 3 in every 50 babies (4–6%) who develop GBS disease die.

Pregnant Women

• About 1 in 4 pregnant women carry GBS bacteria in their body.
• Doctors should test pregnant woman for GBS bacteria when they are 36 through 37 weeks pregnant.
• Giving pregnant women antibiotics through the vein (IV) during labor can prevent most early-onset GBS disease in newborns.
  • A pregnant woman who tests positive for GBS bacteria and gets antibiotics during labor has only a 1 in 4,000 chance of delivering a baby who will develop GBS disease. If she does not receive antibiotics during labor, her chance of delivering a baby who will develop GBS disease is 1 in 200.

• Pregnant women cannot take antibiotics to prevent early-onset GBS disease in newborns before labor. The bacteria can grow back quickly. The antibiotics only help during labor.

Other Ages and Groups

• GBS bacteria may come and go in people’s bodies without symptoms.
• On average, about 1 in 20 non-pregnant adults with serious GBS infections die.
• The rate of serious group B strep disease increases with age:
  • There are 10 cases in every 100,000 non-pregnant adults each year.
  • There are 25 cases in every 100,000 adults 65 years or older each year.
• The average age of cases in non-pregnant adults is about 60 years old.

References

• Centers for Disease Control and Prevention. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Group B Streptococcus, 2018
• Francois Watkins LK, McGee L, Schrag SJ, Beall B, Jain JH, Pondo T, et al. Epidemiology of invasive group B streptococcal infections among nonpregnant adults in the United States, 2008–2016external icon. JAMA Intern Med. 2019;179(4):479–88.
• Nanduri SA, Petit S, Smelser C, Apostol M, Alden NB, Harrison LH, et al. Epidemiology of invasive early-onset and late-onset group B streptococcal disease in the United States, 2006 to 2015: Multistate laboratory and population-based surveillanceexternal icon. JAMA Pediatrics. 2019;173(3):224–33.

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

What is group B streptococcus (GBS)?

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.

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