The study analysed data from nearly 90,000 births over 25 years
The number of premature births has risen significantly but survival rates for babies born early have also improved, a study has found.
The Edinburgh University research found that the risk of neonatal death from premature birth more than halved between 1980 and 2005.
The number of premature babies rose from 54 per 1,000 births between 1980 and 1985 to 63 between 2000 and 2005.
High blood pressure and diabetes were identified as major factors.
Edinburgh University analysed data relating to almost 90,000 births in Scotland between 1980 and 2005.
They also found that stillbirth associated with pre-term births also fell, by 10%.
Researchers hope that a better understanding of the trends and causes behind premature births will help to develop better treatments for expectant mothers.
Improvements in the survival rates of premature babies were found to be greater when births were medically-induced or by pre-planned Caesarean section compared with pre-term births in which labour occurred naturally.
The researchers said the findings supported moves towards more medically-induced early births, with these pre-term deliveries up more than 40%.
This was compared to a 10% increase in early births from natural onset of labour.
The research, published in the journal Public Library of Science Medicine, also found the growing number of expectant mothers with diabetes had resulted in an increase in the numbers of babies born prematurely.
Researchers found a seven-fold increase in premature births where the mothers were diabetic before becoming pregnant.
Premature births linked to gestational diabetes, where expectant mothers develop diabetes during pregnancy, also increased four-fold over the study period.
High blood pressure in expectant mothers, however, remained the major factor linked to pre-term births - although the proportion of babies born prematurely as a result of this condition decreased over the 25-year study period.
A rise in the average age of women becoming pregnant was not found to have affected the incidence of premature births.
Professor Jane Norman, director of the Tommy's Centre for Maternal and Fetal Health Research at the University of Edinburgh, said: "The increase in survival rates for babies born prematurely backs up decisions by doctors to medically induce births to prevent potential complications.
"The increase in diabetes as a factor in premature births is also interesting and may be because there are more women with pre-existing diabetes - which is linked to obesity - as well as better diagnosis of expectant mothers with gestational diabetes."
The study was carried out in collaboration with Information Services Division and NHS Scotland and funded by the Chief Scientist Office, Scottish government and the charity Tommy's.
Premature births are linked to more than 66% of single baby still births, 65% of single baby neonatal deaths and 67% of infants who have a prolonged stay in the neonatal unit.