Asthma has been associated with a prolonged time to pregnancy and a decreased birth rate in a new clinical observation study. Published today (12 February, 2016) in the European Respiratory Journal, the research adds to previous studies that have identified a link between asthma and fertility. The evidence so far has been conflicting and many of the studies have either relied on data from questionnaires or small sample sizes.

The current study investigated 245 women with unexplained fertility problems aged between 23 and 45 years. They underwent asthma and allergy testing and questionnaires during their fertility treatment. 96 women in the study had either an existing doctor's diagnosis of asthma or were diagnosed with asthma when they entered the study. 

The researchers monitored the women during their fertility treatment for a minimum of 12 months, until they had a successful pregnancy, stopped treatment or the observation ended. 

The results found that the median total time to pregnancy was 32.2 months in non-asthmatic women and 55.6 months in those with asthma. Women with asthma also had fewer successful conceptions: 39.6% achieved pregnancy in the asthmatic women compared with 60.4% in the women without asthma. The results also found this trend was more apparent as the women got older. 

Lead author Dr Elisabeth Juul Gade, commented: "This finding in a clinical trial setting adds new weight to the epidemiological evidence suggesting a link between asthma and fertility. We have seen here that asthma seems to have a negative influence on fertility as it increases time to pregnancy and even more so with age. 

"We do not yet know the causal relationship; it may be complex with different types of asthma, psychological well-being, asthma medication and hormones all play a role. Given this new evidence, we believe that clinicians should encourage women with asthma to become pregnant at an earlier age and optimise their treatment for asthma pre-conception. Patient education is also of paramount importance as adherence to treatment may be enhanced if patients are informed of this link."