Study of Treat to Target Versus Routine Care Maintenance Strategies in Crohn's Disease Patients Treated With Ustekinumab

Study investigates benefit of treat to target maintenance treatment strategy versus routine care to test hypothesis that 'treat to target' ustekinumab (UST) maintenance treatment strategy coupled with early endoscopic assessment will result in higher endoscopic response rate after 48 weeks of treatment, compared to pragmatic maintenance treatment strategy. It consists of screening (5 weeks); treatment period (Week 0 to 48); extension period (Weeks 48 to 104) and safety follow up visit (16 weeks after last dose). Participants will be given an option to enter ultrasound sub-study to assess intestinal ultrasound (IUS) parameters indicating transmural changes in response to treatment with UST in participants with Crohn's disease. Study treatment will be unaffected by participation in sub-study which is optional for participants of main study.