The Asthma in Pregnancy Study evaluated the relationship between maternal asthma severity and control. The primary objective was to determine the frequency of preterm delivery <32 weeks among moderate and severe asthmatics compared to non-asthmatic controls. The incidence of small-for-gestational-age infants in women with mild and moderate asthma was a secondary outcome. Other independent variables included type of medications used, race, socioeconomic status, height, weight, parity, nutrition, smoking, other substance abuse, and prenatal care. Secondary outcomes included birth weight and prematurity, maternal pre-eclampsia, gestational hypertension, and asthma morbidity. The study began February 1,1995 and patient recruitment continued for 46 months or less.