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Table 1 Levels of evidence and grades of recommendation (according to the ESMO Clinical Practice Guidelines for fertility preservation in cancer patients [11])

From: Cancer and fertility preservation: international recommendations from an expert meeting

Levels of evidence

I

Evidence from at least one large randomized, controlled trial of good methodological quality (low potential for bias) or meta-analyses of well-conducted randomized trials without heterogeneity

II

Small randomized trials or large randomized trials with a suspicion of bias (lower methodological quality) or meta-analyses of such trials or of trials with demonstrated heterogeneity

III

Prospective cohort studies

IV

Retrospective cohort studies or case–control studies

V

Studies without control group, case reports, experts opinions

Grade of recommendation

A

Strong evidence for efficacy with a substantial clinical benefit, strongly recommended

B

Strong or moderate evidence for efficacy but with a limited clinical benefit, generally recommended

C

Insufficient evidence for efficacy or benefit does not outweigh the risk or the disadvantages (adverse events, costs, etc.), optional

D

Moderate evidence against efficacy or for adverse outcome, generally not recommended

E

Strong evidence against efficacy or for adverse outcome, never recommended