A prospective study of preconception asthma and spontaneous abortion.

PURPOSE:To evaluate the relationships among history of asthma, asthma severity, and spontaneous abortion (SAB). METHODS:Pregnancy Study Online is a preconception cohort study of North American couples. During the preconception period, female participants reported their history of physician-diagnosed asthma, age at first diagnosis, and use of asthma medications in the previous 4 weeks. Asthma severity was classified by medication use proximal to conception, from level 0 to 3 in increasing severity. Pregnancy and SAB were identified using data from follow-up questionnaires. We estimated hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS:Among 6325 participants who conceived, 19% experienced SAB and 17% reported a history of asthma. There was no appreciable association between asthma history and SAB incidence (HR = 0.98; 95% CI: 0.84, 1.14). HRs comparing severity levels 0, 1, and 2-3 with no asthma were 0.82 (95% CI: 0.67, 1.01), 1.20 (95% CI: 0.91, 1.60), and 1.31 (95% CI: 0.97, 1.78), respectively. Among women who conceived without the use of fertility treatment, level 2-3 severity was associated with SAB (HR = 1.39; 95% CI: 1.02, 1.89). CONCLUSIONS:While history of asthma diagnosis was not materially associated with SAB, having severe asthma (based on medication use) was associated with greater SAB risk.