De Buck Van Overstraeten 2017.

Study characteristics
Methods	Retrospective cohort. Study period: 1998 to 2013
Participants	Country: Belgium. CD patients who underwent primary ileocecal resection
Interventions	1. Preoperative anti‐TNF therapy (n= 111) within 12 weeks of surgery 2. Preoperative steroids (n=278) 3. No preoperative anti‐TNF therapy (n=427) 4. No preopera tive steroids (n= 260)
Outcomes	Anastomotic leak within 30 days of surgery
Notes	NOS low risk of bias overall Adjusted ORs for preoperative steroids and anti‐TNF therapy were obtained from multivariate logistic regression model .
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	Patients with CD operated on for terminal ileocecal disease
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospital and time period
Ascertainment of exposure	Low risk	Medical charts reviewed
Demonstration that outcome of interest was not present at start of study	Unclear risk	No information provided
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	Did not control for other medications
Comparability of cohorts (Controlled for additional factor)	Low risk	Corrected for institution and time since first surgical procedure
Assessment of outcome	Low risk	Medical charts reviewed
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	No information provided