The link between pre-term birth and asthma, or wheezing conditions, is higher than was previously thought, a study suggests.
Asthma is already the most common chronic disease in childhood, affecting around 8% of offspring born after a normal-length pregnancy.
With increasing numbers of babies surviving premature birth, childhood asthma is set to become a significant health problem, say scientists.
An estimated 11% of children are now born pre-term.
The research showed average asthma rates rose to 14% in babies born prematurely, defined as at least three weeks early.
Those born more than three weeks before the usual 40-week term were almost 50% more likely than full-term babies to develop asthma. And babies born more than two months early were three times more at risk.
The findings, published in the online journal Public Library of Science Medicine, also suggest that children born prematurely do not outgrow their vulnerability to asthma. The risk of developing asthmatic symptoms was the same for both pre-school and school-age children.
Study leader Dr Jasper Been, from Edinburgh University's Centre for Population Health Sciences, said: "Doctors and parents need to be aware of the increased risks of asthma in premature babies, in order to make early diagnosis and intervention possible.
"By changing the way we monitor and treat children born pre-term, we hope to decrease the future risks of serious breathing problems."
The researchers studied data on around 1.5 million children pooled from 30 studies.
Many premature babies experience breathing problems because their lungs are immature. Previous research has suggested this can lead to asthma, but whether or not it affects long-term risk is unclear.
Dr Samantha Walker, executive director of research at Asthma UK, said: "We know that uncontrolled asthma in pregnant women, amongst other things, can increase the risk of premature birth, which reinforces the need for good asthma management during pregnancy."