Group B Strep and pregnancy

The information below is for you, a friend or a relative who is expecting a baby, planning to become pregnant or has recently had a baby. 

What is group B Strep?

Group B Streptococcus (GBS, group B Strep or Strep B) is a type of bacteria which lives in the intestines, rectum, or vagina of 2 to 4 in every ten women in the UK (20 to 40%). This is often referred to as ‘carrying’ or being ‘colonised with’ group B Strep.

Most women carrying GBS will have no symptoms. Carrying GBS is not harmful to you, but there is a small chance it can affect your baby around the time of birth.

GBS can occasionally cause serious infection in young babies and, very rarely, in babies before they are born. Carrying GBS can also sometimes lead to serious infections for pregnant women, though this is also rare.

How is group B Strep spread?

Group B Strep is not a sexually transmitted disease.

Like many bacteria, GBS can be passed from one person to another through direct contact, for example, hand holding, kissing, close physical contact, etc. As GBS is often found in the vagina and rectum, it can also be passed on during sex.

There are no known harmful effects of carrying GBS. The GBS bacteria do not cause genital symptoms or discomfort. GBS carriage is not a sign of ill health or poor hygiene. Around 20 to 40% of women carry GBS.

Because GBS can be passed from one person to another by skin-to-skin contact, everyone (regardless of whether they know they carry GBS) should wash and dry their hands properly before handling a newborn baby.

How is group B Strep found?

Most women carrying GBS have no symptoms, so GBS is often found by chance through a vaginal or rectal swab test or a urine test.

The NHS does not routinely test all pregnant women for group B Strep.

A test designed specifically to identify whether you carry GBS, known as the Enriched Culture Medium (ECM) test, is becoming more available within the NHS and is widely available privately.

Since September 2017, the Royal College of Obstetricians & Gynaecologists (RCOG) has recommended in their guideline on group B Strep that the ECM test should be used when testing for group B Strep. However, many maternity units still use a standard test (known as the high vaginal swab) that misses up to half of the women carrying group B Strep. Ask your health professionals what is available locally.

There are private home ECM testing kits for GBS you can order.

What could group B Strep mean for my baby?

Many babies come into contact with group B Strep during labour or around birth, and the vast majority will not become ill.

However, there is a small chance that your baby will develop a group B Strep infection. In the UK, about 1 in 1,600 of all babies born develops a GBS infection.

This likelihood of infection is higher if you know you carry GBS; about 1 in every 400 babies born to women known to carry GBS develop a GBS infection.

If the GBS infection is not treated, babies can become seriously ill. But with prompt treatment, most babies will make a full recovery. This makes early detection vital.

The infections that group B Strep most commonly causes in newborn babies are sepsis (infection of the blood and other tissues), pneumonia (infection in the lungs), and meningitis (infection of the fluid and lining around the brain).

Although group B Strep infection can make your baby very unwell, with prompt treatment, most babies will make a full recovery.

Group B Strep infections are most common in newborn babies during their first few days after birth. However, babies can still develop group B Strep infections up to three months of age, and in very rare cases, beyond three months.

To reflect this, group B strep infections are often split into two categories: early-onset and late-onset infections:

Early-onset group B Strep infection

Early-onset group B Strep infections are those in babies up to seven days old, and occur in around 1 in every 1,750 babies in the UK and Ireland.

Of the babies who develop an early-onset GBS infection, 1 in 19 (5.2%) will die.

Of those who survive an early-onset GBS infection, 1 in 14 (7.4%) will have a long-term physical or mental disability.

Late-onset group B Strep infection

Late-onset group B Strep infections develop in babies older than seven days, and occur in around 1 in every 2,700 babies in the UK and Ireland.

Of those who develop a late-onset GBS infection, 1 in 13 (7.7%) will die.

Of those who survive a late-onset GBS infection, 1 in 8 (12.4%) will have a long-term physical or mental disability.

Overall chances and outlook for babies

On average, in the UK and the Republic of Ireland, every month:

• Around 70,000 live babies are born
• 66 babies are diagnosed with a group B Strep infection
  • 40 early-onset + 26 late-onset GBS infection
• of these, 56 babies make a full recovery
  • 35 early-onset + 21 late-onset GBS infection
• 4 babies die from their group B Strep infection
  • 2 early-onset + 2 late-onset GBS infection
• 6 babies survive with long-term physical or mental disabilities
  • 3 early-onset + 3 late-onset GBS infection

Group B Strep and risk of miscarriage or stillbirth

There is evidence that group B Strep can cause late miscarriage (death of the baby between 14 and 24 weeks of pregnancy) and stillbirth (death of the baby after 24 weeks of pregnancy up until the baby is born). We don’t understand why group B Strep causes stillbirths or late miscarriages in some babies but not others.

However, thankfully stillbirths are relatively uncommon in the UK, and group B Strep is not a common cause of them, accounting for around 1% of all stillbirths before labour in high-income countries. So, it is rare that someone carrying GBS will have a stillbirth or late miscarriage caused by GBS.

We’re not aware of any evidence that group B Strep causes earlier miscarriages (before 14 weeks of pregnancy).

Is my baby at risk of group B Strep infection?

Any baby can develop a group B Strep infection, but early-onset group B Strep infection is more likely if…

• your baby is born preterm (before 37 completed weeks of pregnancy) – the earlier your baby is born, the greater the risk;
• you have previously had a baby who developed a group B Strep infection;
• you have a high temperature (or other signs of infection) during labour;
• you have tested positive for group B Strep in this pregnancy;
• you haven’t gone into labour within 24 hours after your waters have broken.

Developing late-onset group B Strep infection is more likely if…

• your baby is born preterm (before 37 weeks of pregnancy);
• you have tested positive for group B Strep in this pregnancy.

There are ethnic differences in group B Strep infection rates. The overall rate of GBS infection for Black babies is 1 in 1,000 live births, which is 51% higher than the rate for white babies at 0.67 per 1,000 live births. For Asian babies, the infection rate is 0.85 per 1,000 live births, which is 28% higher than that for white babies. However, there is variation in infection rates within these broad categories; for example, babies from an Indian background have similar GBS infection rate to white babies.

How can the risk to my baby be reduced?

Most early-onset group B Strep infections (before the baby is seven days old) can be prevented with intravenous antibiotics, sometimes known as a ‘drip’. These will be given to women during labour if their baby has a higher chance of developing an early-onset GBS infection.

If you opt to have the antibiotics during labour, the risk of your baby developing an early-onset GBS infection drops significantly to around 1 in 4,000.

You will be offered intravenous (IV) antibiotics during labour if…

you developed a urine infection during pregnancy caused by group B Strep (it should also have been treated with antibiotic tablets straight away).

• you have tested positive for GBS after a swab from an NHS or other accredited laboratory (see www.gbss.org.uk/test).
• you have previously had a baby who was diagnosed with a GBS infection.
• you develop any signs of infection during labour (e.g. high temperature), even if you don’t know whether you carry GBS. (You will be offered IV antibiotics to treat various infections, including GBS.)
• your labour starts before 37 completed weeks of your pregnancy (premature labour), even if you don’t know whether you carry GBS.

Other situations:

• If you tested positive for GBS during a previous pregnancy and your baby was unaffected, you can be tested when you are 35 to 37 weeks pregnant. If the test result is positive, you will be offered antibiotics in labour. If the test result is negative at this point, the risk of your baby developing early-onset GBS infection is low, and you may choose not to have antibiotics.
• If your waters break after 37 completed weeks of your pregnancy and you are known to carry GBS, you will be offered induction of labour straight away. This is to reduce the time that your baby is exposed to GBS before birth. You should also be offered IV antibiotics.

At present, there are no known methods to prevent late-onset GBS infection (those happening after the baby is seven days old). If you carry GBS, your baby will be monitored and receive treatment if they show signs of GBS infection.

Find out how your baby will be monitored after birth for signs of GBS infection.

If you are worried about your baby, you should urgently contact your healthcare professional and mention any history of GBS when you do.

Related pages

Where to order a group B Strep test

What does my test result mean?

After your baby is born