Effect of Maternal Asthma on the Risk of Specific Congenital Malformations: A Population-Based Cohort Study

BACKGROUND: There is a lack of consensus in the literature about the effect of maternal asthma on the development of congenital malformations. OBJECTIVE: To further examine the association between maternal asthma and the risk of congenital malformations. METHODS: A cohort of 41,637 pregnancies from women with and without asthma who delivered between 1990 and 2002 was reconstructed by linking three Quebec (Canada) administrative databases. All cases of malformations were identified using either the medical services or the hospital databases. The main exposure was maternal asthma, defined by the presence of at least one asthma diagnosis and at least one prescription for an asthma medication at any time in the two years before or during pregnancy. Generalized Estimation Equation models were performed to estimate the adjusted odds ratio (OR) of congenital malformations as a function of maternal asthma. RESULTS: The crude prevalences of any congenital malformation were 9.5% and 7.5% for women with and without asthma, respectively. Maternal asthma was significantly associated with an increased risk of any malformation (OR=1.30; 95% CI: 1.20-1.40) and three specific groups (at the 0.0028 level): nervous system (excluding spina bifida: OR=1.83; 1.37-2.83); respiratory system (OR=1.75; 1.21-2.53); and digestive system (OR=1.48; 1.19-1.85). CONCLUSIONS: Maternal asthma increases the risk of specific groups of congenital malformations. The disease itself, through fetal oxygen impairment, is likely to play a role in this increased risk, but more research is needed to disentangle the relative effect of asthma and medications used to treat this disease. Birth Defects Research (Part A) 88:216-222, 2010. (C) 2010 Wiley-Liss, Inc.