The present study investigates pregnancy outcome in women with IBD and examines the effect of pregnancy on the severity of IBD. Method: A case-control study comparing deliveries by mothers with IBD between January 1988 and January 2005 was performed. For every birth by a mother with IBD, four births by non- IBD mothers were randomly selected and adjusted for ethnicity and year of delivery. Result: During the study period there were 48 deliveries to patients with Crohn’ s disease and 79 deliveries to patients with ulcerative colitis. Higher rates of preterm delivery ( < 37 weeks) were found among patients with IBD as compared to the controls (odds ratios (OR) = 2.2; 95% confidence interval (CI) = 1.3- 3.8). This association remained significant after adjustment for labor induction and multiple gestations, using the Mantel-Haenszel technique (weighted OR = 2.1; 95% CI 1.3- 3.5 and weighted OR = 2.0; 95% CI 1.2- 3.5; P = 0.012; respectively). In addition, these patients had higher rates of fertility treatments (OR = 2.2; 95% CI = 1.1- 4.4). Using a multivariate analysis, controlling for maternal age and fertility treatments, preterm delivery was seen to be significantly associated with IBD (adjusted OR = 2.0; 95% CI = 1.2- 3.5). Perinatal outcomes, such as perinatal mortality, low Apgar scores, and congenital malformations, were comparable to the outcomes in the control group. Conclusion: Maternal IBD is an independent risk factor for preterm delivery. IBD is not associated with adverse perinatal outcome. The present study investigates pregnancy outcome in women with IBD and examines the effect of pregnancy on the severity of IBD. Method: A case-control study comparing deliveries by mothers with IBD between January 1988 and January 2005 was performed. For every birth by a mother with IBD, four births by non- IBD mothers were randomly selected and adjusted for ethnicity and year of delivery. Result: During the study period there were 48 deliveries to patients with Crohn’s disease and 79 deliveries to patients with ulcerative colitis. Higher rates of preterm delivery (<37 weeks) were found among patients with IBD as compared to the controls (odds ratios (OR) = 2.2; 95% confidence interval (CI) = 1.3- 3.8) and multiple gestations, using the Mantel-Haenszel technique (weighted OR = 2.1; 95% CI 1.3-3.5 and weighted OR = 2.0; 95% CI 1.2-3.5; P = 0.012; o Using a multivariate analysis, controlling for maternal age and fertility treatments, preterm delivery was seen to be significantly associated with IBD (adjusted OR = 2.0; 95% CI = 1.1- 4.4) 1.2- 3.5). Perinatal outcomes, such as perinatal mortality, low Apgar scores, and congenital malformations, were comparable to the outcomes in the control group. Conclusion: IBD is an independent risk factor for preterm delivery. perinatal outcome