Objective: The purpose of this study was to test the hypothesis that maternal asthma symptoms and pulmonary function are related to adverse perinatal outcomes. Study design: Asthmatic patients were recruited from the 16 centers of the Maternal Fetal Medicine Units. Forced expiratory volume in 1 second was obtained at enrollment and at monthly study visits, and the frequency of asthma symptoms was assessed from enrollment to delivery. Perinatal data were obtained at postpartum chart reviews. Results: The final cohort included 2123 participants with asthma. After adjustment for demographic characteristics, smoking, acute asthmatic episodes, and oral corticosteroid use, significant relationships were demonstrated between gestational hypertension and preterm birth and lower maternal gestational forced expiratory volume in 1 second. The data did not show any significant independent relationship between asthma symptom frequency and perinatal outcomes. Conclusion: Lower pulmonary function during pregnancy is associated with increased gestational hypertension and prematurity in the pregnancies of women with asthma, which may be due to inadequate asthma control or factors that are associated with increased asthma severity. Objective: The purpose of this study was to test the hypothesis that maternal asthma symptoms and pulmonary function are related to adverse perinatal outcomes. was obtained at enrollment and at monthly study visits, and the frequency of asthma symptoms was assessed from enrollment to delivery. Perinatal data were obtained at postpartum chart reviews. Results: The final cohort included 2123 participants with asthma. After adjustment for demographic characteristics, smoking , acute asthmatic episodes, and oral corticosteroid use, significant relationships were demonstrated between gestational hypertension and preterm birth and lower maternal gestational forced expiratory volume in 1 second. The data did not show any significant independent relationship between asthma symptom frequency and perinatal outcomes. Conclusion: Lower pulmonary function dur ing pregnancy is associated with increased gestational hypertension and prematurity in the pregnancies of women with asthma, which may be due to inadequate asthma control or factors that are associated with increased asthma severity.