Group B streptococcus (GBS) is a common bacteria found in the gastrointestinal tract and vagina of around 30% of people. It usually lives there harmlessly as part of your normal or transient gut and skin flora.
In pregnancy, GBS can cause miscarriage or preterm labour. GBS urinary tract infection also suggest a heavy colonisation of GBS in the vagina, which can enter the uterus after your waters have broken or pass on to the baby as they pass through the vagina.
While GBS is not usually a problem for healthy adults, it can cause serious infection in a newborn. The chance of infection is low, but the consequences can be serious, causing pneumonia, septicaemia, and/or meningitis.
Screening for GBS is not routine in Aotearoa, although some midwives will send a routine urine sample at booking that can be cultured for GBS. Even though it is routine, GBS bacteriuria screening is your choice, and you can decline if you wish. If you wish to have a rectovaginal swab for GBS around 37 weeks, this can be carried out for you via a self-swab or a midwife-collected swab. It takes around 3-4 days for the results to come back, whether as a urine culture or a swab.
If you have a positive GBS culture or risk factors for GBS infection in your baby (such as preterm labour or prolonged rupture of membranes) then you will be offered antibiotics in labour. This is via IV, and will usually be benzylpenicillin unless you are allergic to penicillin.
Like all interventions, IV antibiotics in labour have risks and benefits, and your midwife will discuss these with you if you are being offered this intervention. Some risks include other infections in the baby with resistance to the antibiotics used in your labour, slower microbiome establishment, and allergic reactions to the antibiotic. Benefits can include a lower risk of GBS infection in your baby. Only you can decide which risks and benefits are most important to you.