BACKGROUND AND AIMS: The impact of biologic treatment for inflammatory bowel disease (IBD) during pregnancy and lactation on infant psychomotor development is barely studied. We investigated the effect of exposure to biologics in utero or during breastfeeding on the psychomotor development of offspring during their first year METHODS: The study included patients and infants from DUMBO, an ongoing prospective, observational registry of GETECCU enrolling pregnant women (aged >/=18 years) with IBD from 60 centers across Spain. Mothers were followed-up at each trimester during pregnancy and after delivery. Psychomotor development of infants was assessed using the Spanish version of the Ages and Stages Questionnaire 3rd edition (ASQ-3) during the first year of life. An ASQ-3score below the normal limit in any domain was considered abnormal. RESULTS: In total, 352 children born to 343 women were assessed; 134 infants (38.1%) were exposed to biologics during pregnancy and 80 (22.7%) during lactation, including five who were exclusively breastfed. At 12 months, the proportions of infants with normal ASQ-3 total scores (86% vs 74%; p=0.031) and normal gross motor domain scores (91% vs 81%; p=0.033) were significantly higher in the biologics-exposed versus non-exposed subgroups. Multivariate analysis revealed that preterm birth (OR 0.3; 95% CI 0.1-0.6) and maternal ulcerative colitis (OR 0.5; 95% CI 0.3-0.9) were associated with an increased risk of abnormal ASQ-3. Other variables, including exposure to biologics in utero, had no impact on ASQ-3 scores at month 12. CONCLUSIONS: Exposure to biologics for IBD in utero or during breastfeeding has no negative impact on psychomotor development in infants.