OBJECTIVE: To assess the effects of maternal asthma on pregnancy, analyzing the consequences of the severity of the disease in the impairment of fetal well-being, as well as the related maternal and perinatal complications. METHODS: A retrospective study with 117 pregnancies complicated by maternal asthma and with no other comorbidities, in the period from January, 2005 to December, 2010. Inclusion criteria were as follows: singleton pregnancy; pregnant women diagnosed with asthma prior to pregnancy; initiation of prenatal care before the 28(th) week of pregnancy; birth at this institution; newborn weighing over 500 g and gestational age at delivery of 22 weeks or more; absence of fetal malformations or chromosomal abnormalities; absence of maternal comorbidities. Asthma was classified as intermittent, mild persistent, moderate persistent, or severe persistent. The results of fetal biophysical profile and of Doppler velocimetry of the umbilical artery performed 14 days prior to birth were analyzed. RESULTS: Of the total of 117 pregnant women with asthma, 41 (35.0%) had intermittent, 33 (28.2%) mild persistent, 21 (17.9%) moderate persistent, and 22 (18.8%) severe persistent asthma. There was no significant difference among the groups as to the type of birth: cesarean section was performed in 65.8% of the cases, maternal corticosteroid therapy was used at the moment of birth in 20.5%, the gestational age at birth averaged 38.6 weeks (SD 1.9 weeks), and birth weight averaged 3,056 g (SD 581g). The fetal biophysical profile performed during the antepartum period (n=90, 76.9%) showed a normal result (8 or 10) in 99% of the cases. Doppler velocimetry of the umbilical artery was assessed in 23.9% (n=28) of the pregnant women, and delivered normal results in 100% of the cases. The use of systemic corticosteroid therapy was significantly (p<0.001) different among the intermittent (4.9%), mild persistent (9.1%), moderate persistent (28.6%), and severe persistent (45.5%) groups. Regarding the beginning of birth, there was a higher proportion of elective cesarean section in the groups with moderate persistent asthma (52.5%) and severe persistent (54.6%) when compared to the intermittent (21.9%) and mild persistent (24.2%) groups (p=0.039). CONCLUSION: The severity of maternal asthma does not appear to have any direct influence on perinatal outcomes, and does not compromise fetal well-being. Active conduct to enable a better maternal clinical condition provides a favorable prognosis for pregnancy complicated by asthma.