Fertility Outcomes in Women With Asthma: A Danish Nationwide Cohort Study

Background: Asthma is common among women of reproductive age. Prior studies have revealed an association between asthma and fertility by reporting prolonged time to pregnancy and lower fecundability. Objective: To investigate fertility in women treated with asthma medication compared with women without asthma. Methods: All women born between 1976 and 1999, who were living in Denmark on their 18th birthday, were followed from 1994 to 2017. Asthma was defined as repeated fulfillment of asthma medication prescriptions, and severity was classified according to the Global Initiative for Asthma guidelines (GINA). Outcome was fertility treatment in women with asthma compared with women without asthma, applying a Cox regression model adjusted for age, calendar year, and education. Results: The cohort comprised 765,606 women followed up, starting on their 18th birthday, for a median time of 10.8 years (interquartile range: 5.3-17.5 years). Compared with women without asthma, women with asthma had a comparable proportion giving birth during follow-up, slightly more experienced fetal loss (17.0% vs 15.8%), and required fertility treatment (5.6% vs 5.0%). The risk of fertility treatment was significantly higher in women with asthma (hazard ratio [HR]: 1.10, 95% confidence interval [CI]: 1.07-1.14). Women on GINA treatment steps 4 and 5 had an even higher risk of fertility treatment (HR: 1.59, 95% CI: 1.41-1.80) and, likewise, women with ≥3 prior exacerbations of asthma (HR: 1.36, 95% CI: 1.17-1.58). Conclusion: Women with asthma have an increased use of fertility treatment, which correlates with asthma severity and exacerbation burden. However, asthma does not seem to affect number of live births.