1. Methodological quality of included cohort studies.

Risk of bias domain*		Baudry 2014	Boucher 2016	De Cruz 2013	Bordeianou 2011	Guo 2018
Selection	Representativeness of the exposed cohort	★	★	★	★	★
	Selection of the non‐exposed cohort	‐	★	★	★	‐
	Ascertainment of exposure	★	★	‐	★	★
	Outcome was not present at start of study	★	★	★	★	★
Comparability	Comparability of cohorts (design or analysis) *	★ ‐	★ ‐	‐ ‐	★ ‐	★ ‐
Outcome	Assessment of outcome	★	★	★	★	★
	Length of follow‐up	★	★	★	★	‐
	Adequacy of follow‐up	★	★	★	‐	★

Methodological quality of included cohort studies, according to the Newcastle‐Ottawa Scale (NOS)*.

* NOS allows a semi‐quantitative assessment of the risk of bias. The scale ranges from zero to nine stars. The overall methodological quality of each study was considered "Low" whether in at least one of the items the risk of bias was judged as high (zero stars) (Baudry 2014; Bordeianou 2011; De Cruz 2013; Guo 2018).