|Premature birth can have long-term health effects for both mothers and children|
A major cause of premature birth - where waters break too soon, triggering labour - may be caused by specific bacteria, according to research.
The findings could lead to screening and possible treatment for women at risk of early labour, says a US team.
The study, published in the journal PLOS ONE, suggests certain bacteria may lead to thinning of the membranes around the baby, causing them to tear.
Early rupture of membranes causes almost a third of all premature births.
The membranes that make up the sac that holds the baby usually break at the start of labour.
If a mother's waters break before the baby has reached full term, the medical term is preterm premature rupture of the membranes (PPROM).
If this happens early, before contractions start, it can - but does not always - trigger early labour.
Researchers at Duke University School of Medicine have found high numbers of bacteria at the site where membranes rupture, which are linked with the thinning of membranes.
If the bacteria are the cause rather than the consequence of early membrane rupture, it may be possible to develop new treatments or screen for women at risk, they say.
Study author Amy Murtha, associate professor of obstetrics and gynaecology at Duke University School of Medicine, said: "For instance, if we think that certain bacteria are associated with premature rupturing of the membranes, we can screen for this bacteria early in pregnancy.