Impact of maternal asthma on perinatal outcomes: a two-stage sampling cohort study.

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.