Scientists want the use of progesterone therapy to prevent premature births to be reviewed while alternative solutions are found.

A widely used hormone therapy that is supposed to prevent premature births does not work, researchers claim.

Scientists are calling for use of the treatment to be reviewed while a greater effort is made to find alternative solutions.

Previous studies had suggested that treating pregnant women with the hormone progesterone can help to stop them giving birth too early.

But a new trial involving more than 1200 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 to premature birth rates and offered no notable health benefit either to mothers or babies.

Trial leader 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."

More than 64 hospitals around the UK took part in the research, reported in The Lancet medical journal.