- Objective: 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.