Campaigners are calling for a test which could potentially save the lives of newborn babies to be available on the NHS.
Group B strep is relatively common
Group B streptococcus (GBS) is the most common cause of life-threatening infection in newborn babies in the UK. It can lead to meningitis, septicaemia or pneumonia.
Up to 700 babies a year are infected with GBS. Of these, up to 100 die and another 20 are left with serious long-term mental or physical problems.
The charity Group B Strep Support is calling for the NHS to adopt routing testing in late pregnancy.
The test, which costs £18, is currently only available privately.
At the moment, babies are sent for testing if they show signs of infection.
It has been estimated that there may be up to three times the numbers of cases of GBS as are detected.
Campaigners say routine screening would be a more effective method of picking up cases.
Professor Robert Feldman, an expert in neonatal infection at Imperial College, London and chairman of the charity's medical advisory panel, said: "Other countries, including the USA, routinely test women late in pregnancy for GBS using the reliable enrichment culture method.
"Scientific evidence shows that screening with this method - and then giving intravenous antibiotic injections from the onset of labour to those carrying GBS, those with a history of GBS and those delivering prematurely - will prevent most GBS infections in new-born babies.
"But this is not done in the UK. The tests used here for detecting GBS are highly insensitive.
"A swab taken from a woman carrying the infection will give an incorrect negative result up to half of the time."
A London laboratory, OmniLabs Pathology Services, is now offering the more reliable test privately for the first time.
It must be authorised by a health professional, who can obtain a free screening pack from the laboratory with advice on the procedure.
Vaginal and rectal swabs are taken by the health professional or by the pregnant woman herself at 35-37 weeks of pregnancy.
For £18 the laboratory will send the result to the health professional within three working days.
Professor Feldman said: "Every pregnant woman should be given information about GBS.
"Yet most people have never heard of it. This ignorance is causing babies and their families to suffer needlessly."
David Cameron, MP for Witney, has tabled an Early Day Motion in parliament calling on the government to investigate ways to prevent GBS infection as a matter of urgency. The motion has been backed by around 100 MPs.
But both the Royal Colleges of Midwives and Obstetricians believe that offering all pregnant women screening for GBS is not clinically merited, or cost effective.
Dr Christine McCartney, of the Health Protection Agency, said: "At this moment in time we cannot recommend universal screening for GBS.
"There are some serious issues that have to be considered, not least the side effects of administering antibiotics to women in labour.
"Currently there is a committee reviewing all the available expert advice and evidence."