BACKGROUND & AIMS: Endoscopy is an integral part of the investigation and management of gastrointestinal disease. We aimed to examine outcomes of pregnancies for women who underwent endoscopy during their pregnancy. METHODS: We performed a nationwide population-based cohort study, linking data from the Swedish Medical Birth Registry (for births from 1992 through 2011) with those from the Swedish Patient Registry. We identified 3052 pregnancies exposed to endoscopy (2025 upper endoscopies, 1109 lower endoscopies, and 58 endoscopic retrograde cholangiopancreatographies). Using Poisson regression, we calculated adjusted relative risks (ARRs) for adverse outcomes of pregnancy according to endoscopy status using 1,589,173 unexposed pregnancies as reference. To consider the effects of disease activity, we examined pregnancy outcomes (preterm birth, stillbirth, small for gestational age, or congenital malformations) in women who underwent endoscopy just before or after pregnancy. Secondary outcome measures included induction of labor, low birth weight (<2500 g), cesarean section, Apgar score <7 at 5 minutes, and neonatal death within 28 days. To consider intrafamilial factors, we compared pregnancies within the same mother. RESULTS: Exposure to any endoscopy during pregnancy was associated with an increased risk of preterm birth (ARR, 1.54; 95% confidence interval [CI], 1.36-1.75) or small for gestational age (ARR, 1.30; 95% CI, 1.07-1.57) but not of congenital malformation (ARR, 1.00; 95% CI, 0.83-1.20) or stillbirth (ARR, 1.45; 95% CI, 0.87-2.40). None of the 15 stillbirths to women with endoscopy occurred <2 weeks after endoscopy. ARRs were independent of trimester. Compared to women with endoscopy <1 year before or after pregnancy, endoscopy during pregnancy was associated with preterm birth (ARR, 1.16) but not with small for gestational age (ARR, 1.19), stillbirth (ARR, 1.11), or congenital malformation (ARR, 0.90). Restricting the study population to women having an endoscopy during pregnancy or before/after, and only analyzing data from women without a diagnosis of inflammatory bowel disease, celiac disease, or liver disease, endoscopy during pregnancy was not linked to preterm birth (ARR, 1.03; 95% CI, 0.84-1.27). Comparing births within the same mother, for which only 1 birth had been exposed to endoscopy, we found no association between endoscopy and gestational age or birth weight. CONCLUSIONS: In a nationwide population-based cohort study, we found endoscopy during pregnancy to be associated with increased risk of preterm birth or small for gestational age, but not of congenital malformation or stillbirth. However, these risks are small and likely due to intrafamilial factors or disease activity.