Emily Cato reports on the trial from St Thomas's Hospital London

Around 100 babies a day or 40,000 a year are born prematurely in the UK.

Premature birth is a major risk factor for neonatal deaths.

As part of National Pregnancy Week which begins on 6 September, the charity Tommy's Campaign is appealing for 4,000 pregnant women to come forward to take part in a trial which could halve the risk of premature birth.

The charity says an infection caused by the protein fetal fibronectin could be behind as many of half of all premature births.

Research has shown that the presence of the protein in the vaginal secretions of women who have passed their 23rd week of pregnancy is a good indicator of premature birth.

Antibiotic

The trial, known as PREMET, will treat women with the antibiotic metronidazole which is thought to prevent the infection and to be safe for pregnant women, although it does have side effects.

Women taking part in the trial must be under 23 weeks through their pregnancy, have a history of miscarriage or premature birth or have had cervical surgery since their last pregnancy.

The trial will be carried out in six hospitals in the south-east of England.

Tommy's Campaign's Professor of Fetal Health, Lucilla Poston, said: ""We will be testing the theory that infection in mid-term pregnancy is a major factor in triggering premature labour.

"If we can successfully identify and treat this suspected infection, we believe we will be on the way to preventing many premature births."

A three day international conference on the causes and prevention of premature birth will take place from September 7 as part of National Pregnancy Week.