The World Health Organization estimates that 15 million babies are born premature every year, which means they are born before 37 weeks. But new research suggests that risks are higher than previously thought for preterm babies to develop childhood asthma, compared with their full-term counterparts.

Publishing their results in the journal PLoS Medicine, the researchers studied data on more than 1.5 million children around the world.

They used information on patients born since the 1990s from 30 studies, which came from six continents. The majority of the studies came from Europe.

Preterm babies often encounter breathing problems because their lungs are immature, the authors note. They drew from previous research on preterm children born between the 1960s and 1980s, which showed that many of them developed asthma.

However, the researchers say it was unclear whether improved care for preterm babies since then has affected the long-term risk of developing asthma.

Asthma is the most common chronic disease in children, and the team notes that because an increasing number of preterm babies survive birth, the condition is becoming a “significant health problem.”

Overall, the study revealed that while asthma affects 8% of children born at full term, it affects 14% of preterm babies.

In detail, the team found that babies born before 37 weeks were 50% more likely to develop asthma, and those born 2 months early were three times as likely to develop asthma, compared with full-term babies.

Additionally, risks of developing the breathing condition were the same for preschoolers and school-age children, which suggests children who are born early do not outgrow the risk.

“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,” says Dr. Jasper Been, lead study author from the University of Edinburgh’s Centre for Population Health Sciences in Scotland.

Dr. Been adds:

By changing the way we monitor and treat children born preterm, we hope to decrease the future risks of serious breathing problems, including asthma. Our findings should help find better ways to prevent and treat asthma and asthma-like symptoms in those born preterm.”

The authors say the results of their study provide “compelling evidence” that preterm birth increases asthma risks, and they note that future research “needs to focus on understanding underlying mechanisms, and then to translate these insights into the development of preventive interventions.”

But Dr. Samantha Walker, executive director of research and policy at Asthma UK, emphasizes the importance of current asthma medications:

“Standard asthma medicine is very safe to use in pregnancy, and by far the most important way to reduce this risk is for pregnant women to take their medication as prescribed.”

She adds that maintaining a healthy weight, staying active, avoiding stress and not smoking are also important measures to keep in mind.

When asked about any further research the team has planned, Dr. Been told Medical News Today:

An important factor that causes both preterm birth and asthma, particularly in those born preterm, is tobacco smoke exposure before birth. Our current research focuses on evaluating interventions to address this issue.”

In other asthma news, a study recently suggested that secondhand smoke is linked to hospital readmission for asthmatic children. The authors of that study believe their findings could prompt insurance companies to give incentives to parents or guardians who quit smoking.