To conduct a collaborative program of research on asthma and pregnancy consisting of two studies: the Asthma in Pregnancy Study (APS) was an observational study to evaluate relationships between asthma severity and treatment programs and perinatal outcome, and the Asthma Therapy in Pregnancy Trial (ATPT) was a randomized clinical trial of inhaled beclomethasone versus theophylline in the treatment of moderate asthma during pregnancy. Both studies were conducted in the Maternal-Fetal Medicine Unit (MFMU) Network, an ongoing group of participating obstetric centers supported by the National Institute of Child Health and Human Development. Studies were co-funded by the NHLBI.