Babies born early are at risk of serious problems, including breathing issues, heart problems and learning difficulties.
Now scientists have found that placing a small ring around the cervix half way through the pregnancy cuts the risk of a baby being born very prematurely.
High-risk women who received the device were 52% less likely to give birth before 34 weeks of pregnancy than those who did not use the device, said the team from the University of Naples.
They believe the silicone ring, called a cervical pessary, keeps the cervix closed so the baby stays in the womb for longer.
It does this by slightly adjusting the direction of the cervical canal, so the weight of the baby does not force it open too early.
Writing in the Jama medical journal, the scientists said the cervical pessary was a silicone device that had been used to prevent spontaneous pre-term birth.
The leading hypotheses for its mechanism of action were that the pessary helped keep the cervix closed and changed the inclination of the cervical canal so that the pregnancy weight was not directly above the internal opening.
The study involved 300 women who were thought to be at risk of having a premature baby because early scans had shown they had a short cervix, a known risk factor.
Half had a cervical pessary fitted at roughly 20 weeks of pregnancy, and the other half carried on as normal.
The ring was removed at 37 weeks, unless the woman had shown heavy bleeding or other side effects earlier.
Of those who had the ring inserted, only 7.3% gave birth before 34 weeks, compared with 15.3% of those who did not have the device.
The scientists wrote: "Use of a cervical pessary, compared with no pessary use, resulted in a lower rate of spontaneous pre-term birth at less than 34 weeks of gestation."
Women who took part reported only minor side effects.
The scientists said their study had been relatively small, and called for far larger trials to confirm the results.
An editorial by doctors at the University of Utah, published in the same journal, said pessaries were an especially attractive treatment because they were relatively inexpensive, were easy to use, could be made widely available, and had relatively few adverse effects.
"Based on these data, clinicians may contemplate recommending pessaries for all women with a short cervix,” the journal said.
Until now there has not been much evidence about the effectiveness of the device, so while it is sometimes used on the NHS, women at risk of early labour are more likely to be treated with a cervical stitch.
This procedure involves stitching tape around the cervix to keep it closed. - Daily Mail