17/11/2025
In the UK, around 8% of pregnancies result in preterm birth (before 37 completed weeks of pregnancy). Preterm babies have less developed immune systems and are more vulnerable to infections, including group B Strep (GBS). For this reason, UK guidelines recommend intravenous antibiotics for anyone in preterm labour, whether or not they are known to carry GBS.
GBS bacteria can occasionally infect a baby in the womb and may trigger preterm labour, though this is uncommon and is usually linked to maternal infection. Some studies suggest that carrying GBS in pregnancy may increase the chance of preterm birth, but the evidence isn’t robust and more research is needed. However, there is clear evidence of increased risk when GBS causes a urinary tract infection during pregnancy.
There are no proven ways to prevent GBS-related preterm labour, but giving intravenous antibiotics during preterm labour significantly reduces the risk of early-onset GBS infection developing in the baby (within the first 7 days of life).
If your pregnancy is progressing normally, there is no reason to suspect group B Strep infection in your baby. If you have any concerns during pregnancy (including reduced fetal movements), speak to your midwife first. If they are unavailable, contact your maternity unit.
