Most pregnant women who carry group B streptococcus (GBS) bacteria have healthy babies. However, there's a small risk that GBS can pass to the baby during childbirth.
Sometimes GBS infection in newborn babies can cause serious complications that can be life threatening, but this is not common.
Extremely rarely, GBS infection during pregnancy can also cause miscarriage, early (premature) labour, or stillbirth.
GBS is one of many bacteria that can be present in our bodies. It doesn't usually cause any harm. When this happens it's called "carrying" GBS or being colonised with GBS.
It's estimated about one pregnant woman in five in the UK carries GBS in their digestive system or vagina.
Around the time of labour and birth, many babies come into contact with GBS and are colonised by the bacteria. Most are unaffected, but a small number can become infected.
If a baby develops GBS infection less than seven days after birth, it's known as early-onset GBS infection. Most babies who become infected develop symptoms within 12 hours of birth.
Most babies who become infected can be treated successfully and will make a full recovery.
However, even with the best medical care the infection can sometimes cause life-threatening complications, such as:
One in 10 babies born with GBS will die from the infection. Another one in five babies who survive the infection will be affected permanently. Early-onset GBS infection can cause problems such as cerebral palsy, deafness, blindness, and serious learning difficulties.
Rarely, GBS can cause infection in the mother – for example, in the womb or urinary tract, or – more seriously – an infection that spreads through the blood, causing symptoms to develop throughout the whole body (sepsis).
The Royal College of Obstetricians and Gynaecologists (RCOG) has published guidance for healthcare professionals on preventing early-onset GBS infection. For more information, see Is my baby at risk of early-onset GBS infection?.
If you've previously had a baby with GBS, your maternity team will either monitor the health of your newborn baby closely for at least 12 hours after birth, or treat them with antibiotics until blood tests confirm whether or not GBS is present.
Late-onset GBS infection develops seven or more days after a baby is born. This isn't usually associated with pregnancy. The baby probably became infected after the birth – for example, they may have caught the infection from someone else.
GBS infections after three months of age are extremely rare.
Breastfeeding doesn't increase the risk of GBS infection and will protect your baby against other infections.
Read the answers to more questions about pregnancy.