Group B Streptococcus is a normal bacteria that is present in the vagina of up to 30% of women. The most important concern about GBS is the disease called early neonatal Group B streptococcal septicaemia. This occurs after the baby passes through the birth canal and the infection spreads to his or her blood stream. One third of babies affected develop meningitis (an infection of the lining of the brain) and half of these babies will be brain-damaged. 20-30% will die.
Not all mothers that carry the bug pass it to their baby (approximately 35-50%) and not all babies that catch the bug actually develop the signs of infection (only 0.2-2%).
There are some well identified risk factors for a baby developing GBS disease. As well as a positive swab during pregnancy, the following factors lead to a much higher chance of infection (about 50/1000 as compared to 0.3/1000), and may lead to a suggestion for antibiotic treatment during labour:
- Prolonged rupture of membranes (>18-24h)
- Preterm labour (<37w)
- Rupture of membranes before 37 weeks
- Temperature during labour
- GBS found in the urine
- Previous infant with group B strep disease
Some countries screen mothers to check if they carry GBS (US, Australia) but other countries have looked into this and found it to be not appropriate given the rate of neonatal infections (New Zealand, UK). Either way, women with more than one risk factor should receive antibiotics during labour and it should definitely be advised if a woman has had a GBS urine infection or an earlier baby had GBS infection.
See also this teaching resource for health professionals about GBS and pregnancy for other scenarios and advice.