The Asthma Therapy in Pregnancy Trial was a randomized, double-blind, controlled clinical trial which began recruitment in November, 1996, with enrollment lasting 44 months. Patients were randomized to receive either active oral theophylline and a placebo beclomethasone inhaler or an active beclomethasone inhaler and placebo oral theophylline. Albuterol was used for relief of symptoms. The primary outcome measure was incidence of Emergency Department visits or hospitalizations during pregnancy. Secondary outcome measures included birth weight, incidence of small-for-gestational-age infants, gestational hypertension, pre-eclampsia, lung function, daily peak flow, and quality of life. Patients were seen monthly for measurements of fetal growth, morbidity, and lung function. Extensive interviews were conducted with each patient at the first prenatal visit, in the third trimester, and shortly before birth.