Asthmatic women may have more trouble getting pregnant, according to study results in the current issue of the European Respiratory Journal.

Researchers at Bispebjerg University Hospital in Denmark asked 15,250 twins (aged 12–41 years) to complete a questionnaire, including questions about the presence of asthma and fertility. In analyzing the results, investigators discovered asthma was associated with increased time to pregnancy, particularly in those over the age of 30. The association remained significant after adjustment for age, age at menarche, BMI, and socioeconomic status, according to the team.

“The negative effect of asthma on fertility increases with age and is growing with disease intensity, indicating that a systemic disease characterized by systemic inflammation also can involve reproductive processes,” the authors concluded.