Yamamoto 2016.

Study characteristics
Methods	Retrospective multicenter (7 institutions) cohort. Study period: 2008 to 2013
Participants	Countries: Japan, Brazil and Italy. CD patients who underwent ileocolonic resection with primary anastomosis. Patients who had covering ileostomy or with insufficient data for analysis were excluded
Interventions	1. Preoperative steroids (n= 68) 2. Preoperative immunomodulators (n= 65) 3. Preoperative biologics (n= 79) within 8 weeks of surgery 4. No preoperative steroids (n= 163) 5. No preoperative immunomodulators (n= 166) 6. No preoperative biologics (n= 152)
Outcomes	Anastomotic leak, intraabdominal abscess, fistula within 30 days of surgery
Notes	NOS low risk of bias overall Adjusted ORs for preoperative steroids, immunomodulators and biologics were obtained from multivariate analysis.
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	CD patients who underwent ileocolonic resection with primary anastomosis from 2008 to 2013
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospital and time period
Ascertainment of exposure	Low risk	Data was obtained from a prospectively maintained database
Demonstration that outcome of interest was not present at start of study	High risk	43% of patients had perforating disease at baseline
Comparability of cohorts (Controlled for critical factor/other medications)	Low risk	Controlled for steroids, immunosuppressants, biologics
Comparability of cohorts (Controlled for additional factor)	Low risk	Also controlled for age, gender, behavior of CD, smoking, previous resections, blood transfusions, surgical approach and type of anastomosis
Assessment of outcome	Low risk	Data was obtained from a prospectively maintained database
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Low risk	Patients with insuffi ci ent data for analysis were excluded