Appendix 1: Levels of evidence used to rate studies of the treatment of hypertensive disorders in pregnancy and to grade recommendations*

Levels of evidence Randomized controlled trial (RCT) that demonstrates statistically significant difference in at least 1 important outcome (e.g., survival or major illness) OR If difference is not statistically significant, an RCT with adequate sample size to exclude 25% difference in relative risk with 80% power, given the observed results RCT that does not meet the level I criteria Nonrandomized trial with contemporaneous control subjects selected by some systematic method (i.e., not selected by perceived suitability for one of the treatment options for individual patients) OR Subgroup analysis in an RCT Before–after study or case series (at least 10 patients) with historical control subjects drawn from other studies Case series (at least 10 patients) without control subjects Case report (fewer than 10 patients)

Grading system for recommendations The recommendation is based on 1 or more studies at level I The best evidence available was at level II The best evidence available was at level III The best evidence available was lower than level III and included expert opinion

*Reproduced, with permission, from: Sackett DL. Rules of evidence and clinical recommendations on use of antithrombotic agents. Chest 1989;95(2 suppl 2):2S-4S.

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