There are conflicting results concerning the impact of maternal asthma during pregnancy on perinatal outcomes. The present study investigated the associations between maternal asthma during pregnancy and the risk of a small-for-gestational-age (SGA) infant, a low-birth-weight (LBW) infant, and preterm birth. A population-based cohort of 40,788 pregnancies from asthmatic and non-asthmatic women was reconstructed through the linking of three Quebec (Canada) administrative databases between 1990 and 2002. A two-stage sampling cohort design was used to collect additional information by way of a mailed questionnaire. The generalized estimation equation models were used to obtain adjusted odds ratios of SGA, LBW and preterm birth comparing asthmatic and non-asthmatic women. The cohort included 13,007 pregnancies from asthmatic and 27,781 pregnancies from non-asthmatic women. Final estimates showed that the odds of SGA (odds ratio: 1.27, 95% confidence interval: 1.14, 1.41), LBW (1.41: 1.22, 1.63) and preterm delivery (1.64: 1.46, 1.83) were significantly higher among asthmatic than non-asthmatic women. Mothers with asthma during pregnancy are more likely to have SGA, LBW, or preterm birth infants than non-asthmatic women. These results can be more easily generalized to women with lower socio-economic status since the cohort under represents women with high socio-economic status.