All pregnant women who go into labour early should be given antibiotics to protect their baby from a potentially deadly infection.
Hundreds of newborn babies a year in the UK catch Group B Strep (GBS).
Two in every 20 infected babies develops a disability and one in every 20 dies.
The Royal College of Obstetricians and Gynaecologists says any woman who goes into labour before 37 weeks should be offered antibiotics as a precaution.
Group B Strep bacteria can live harmlessly in the lower vaginal tract – about one in four women has it – and it can be passed on to the baby during delivery.
Most women will not realise they are a carrier.
The updated guidelines from the RCOG say pregnant women should be given information about the condition to raise awareness.
They also say women who have tested positive for GBS in a previous pregnancy can be tested at 35 to 37 weeks in subsequent pregnancies to see if they also need antibiotics in labour.
But they do not go as far as recommending routine screening of mothers-to-be.
The RCOG says there is no clear evidence that this would be beneficial, as previously stated by the government’s National Screening Committee but campaigners disagree.
Group B Strep Support would like every pregnant woman to be offered the opportunity to be tested for the bacteria.
Chief executive Jane Plumb said: “The RCOG guideline is a significant improvement on previous editions, however, the UK National Screening Committee still recommends against offering GBS screening to all pregnant women, ignoring international evidence that shows such screening reduces GBS infection, disability and death in newborn babies.”