Alternative solutions are being worked out to prevent premature births as the usual hormone therapy with progesterone does not seem to work.
Previous studies had suggested that treating pregnant women with the hormone progesterone can help stop them giving birth too early.
Professor Alan Cameron, vice president of clinical quality at the Royal College of Obstetricians and Gynaecologists (RCOG), said: "Around 60,000 babies are born prematurely each year in the UK and many suffer lifelong consequences as a result.
‘Vaginal progesterone therapy may help reduce the risk for premature birth in cases of short cervix and if it is the first baby while, progesterone shots are given for later pregnancies.’
A new trial involving more than 1,200 women - the largest ever conducted to assess the therapy - indicates that while the treatment is harmless, it does nothing to reduce the risk of premature birth.
Researchers recruited women who were considered to be at an increased risk of premature delivery, either because they had previously given birth to a pre-term baby or because they had lost a baby late in pregnancy.
Half the women were given progesterone while the rest received a dummy "placebo" pill.
The team found that treatment with progesterone made no difference in premature birth rates and offered no notable health benefit either to mothers or babies.
Professor Jane Norman, director of the Tommy's Centre for Maternal and Foetal Health at the University of Edinburgh, said, "Babies born too early have a much greater risk of short-term and long-term health problems. We need to find new strategies that help mums carry their babies to term."
"This study will be an important resource for any future guideline revision, and we anticipate incorporation of the data provided by the new study into an overview of existing studies of the use of vaginal progesterone, which will assist in providing the best advice to women and those caring for them."