Group B Streptococcus (GBS) is one of the many bacteria that live in our bodies. 20-25% of women are colonized with GBS in vagina or gastrointestinal tract. In most cases this bacteria does not cause harm. If you are found to carry GBS while healthy, this is not considered a disease that needs treatment. However, GBS can be passed from the mother to the baby during labour. 40-50% of babies born to GBS positive mothers can become colonized with GBS. Some of these babies will develop severe infections such as sepsis, pneumonia, meningitis. 14% of babies with early onset GBS disease can die.
GBS can be simply detected by taking a swab from vagina and anus. It is recommended that pregnant women have a GBS swab between 35 and 37 weeks. If the swab is found to be positive, IV antibiotics can be given to women when they are in labour or have ruptured membranes. Without antibiotics 1in 200 babies of GBS positive mothers will develop GBS disease. The risk of early onset GBS disease can be reduced by 80% with the use of antibiotics in labour.
Intravenous Penicillin is the antibiotic of choice and it is given every 4 hours once labour establishes or membranes have ruptured. An alternative antibiotic can be used for women allergic to Penicillin. Taking antibiotics before labour is not beneficial and it will not prevent GBS disease. Women found to be GBS positive on a swab or in urine during earlier gestation are treated in the same way. There is no benefit in repeating the swab again later in pregnancy.
If a woman’s GBS status is unknown at the time of labour onset, treatment should occur according to clinical risk factors. Risk factors in labour for early onset GBS disease include:
- Labour or ruptured membranes before 37 weeks
- Fever greater than 38 degrees
- Prolonged rupture of membranes for more than 18 hours
- Previous child with GBS disease
Using antibiotics in labour is safe. There is a very small risk of severe allergic reaction (anaphylaxis) in the mother. This risk is less than 1in 2000, which is lower than the risk of a baby dying from GBS disease. Other milder side effects for the mother can include rash, nausea or diarrhoea. Alternative antibiotics will be used if you have a known Penicillin allergy. There are no serious adverse effects for the baby. The antibiotic treatment does not affect the way you plan to feed your baby.
Babies of GBS positive mothers will also require observations ie. temperature, heart rate and respiratory rate before each feed in the first 24 hours of life. No antibiotics are usually prescribed for babies unless they are unwell.