Breathing problems are among the most common problems that babies born preterm have after birth, and a new study of over 2.6 million people from Finland and Norway shows that such lung problems may extend at least up to middle age. 

The study, published in European Respiratory Journal, found that babies born preterm are more likely to have asthma or chronic obstructive pulmonary disease (COPD) in adulthood. 

Births before 37 weeks of pregnancy are counted as preterm birth. The highest risk for asthma or COPD was in individuals who were born extremely preterm, before gestational age 28 weeks. Their risk was around three-fold compared to those born full-term at gestational age 39 to 41 weeks.

“The risk decreased gradually as gestational age increased, but individuals who were born close to term, at gestational age 37 to 38 weeks, had still a slightly increased risk compared to the full-term. We also observed that the risk pattern was similar for men and women. However, the risk was up to eight-fold for those who had bronchopulmonary dysplasia in infancy,” says Anna Pulakka, PhD, lead author from Finnish Institute for Health and Welfare (THL), in a press release.

Professor Kari Risnes from Norwegian University for Science and Technology NTNU says in a press release, “Preterm birth affects lung health in many ways, and earlier studies have established that preterm birth is a risk factor for lung health in childhood. The current study shows that the risk extends at least up to middle age.”

Increased risk for asthma and COPD was independent of many factors that are related to preterm birth and asthma, such as socioeconomic status, age or asthma of the mother, prenatal disorders, or mother’s smoking during pregnancy.

“Other than smoking of the mother during pregnancy, we did not have information about smoking of the people included in the study. In earlier studies we have seen that people born preterm do not smoke more than people born full-term, thus smoking is not likely to explain our results,” says Pulakka in a press release. “Smoking is still a major risk factor for asthma and especially COPD and quitting smoking is important for all.”

The research team used national birth registers of all people born in Finland from 1987 to 1998 and in Norway from 1967 to 1999. Their health records were followed up until they were at maximum 29 years old in Finland and 50 years old in Norway. During the study period, around 5% of the children both in Finland and Norway were born preterm. After 18 years of age, about 41,300 people (1.6%) had asthma and about 2,700 (0.1%) had COPD.

“We only studied asthma treated in specialist care, which is why we caught only the more severe end of the disease in this study, and not all who have asthma. The low rates of COPD are additionally explained by the young age of the population in this study,” says professor Eero Kajantie, DMedSc, from THL, in a press release. “Our message to health professionals is that medical history of patients presenting with respiratory symptoms should include birth conditions such as being born preterm.”

The study was a collaboration between the Finnish Institute for Health and Welfare THL, Norwegian University for Science and Technology NTNU, and the University of Oulu.