Supporting information
Box S1. Search strategy
Box S2. Usefulness criteria checklist
Box S3. Details on the interpretation of the eight usefulness criteria
Table S1. List of systematic reviews and randomised controlled trials included
Figure S1. a. Distribution of studies published by year
b. Cumulative number of studies per continent over time.
Table S2. Characteristics of included randomised controlled trials (total) and stratified by Impact Factor (IF) below and above 4, and publication before and after 2010 in high impact factor journals.
Table S3. Details on intervention and controls by study focus (preterm birth prevention primary or secondary aim)
Table S4 . Usefulness criteria overall and stratified on publications before 2000, between 2000-2009 and between 2010-2019; impact factor below and above 4; and publications with impact factor above 4 published after 2010.
Figure S2. Distribution of number of trials (y-axis) with the reported incidence (%) of preterm birth (birth <37 weeks of gestation).
Figure S3. Histograms with relative risk reduction (A) and absolute risk reduction (B) for the 143 studies with a complete power calculation with a negative relative or absolute risk reduction for an increase in the incidence (e.g., increase in the proportion preterm birth >37 weeks), and a positive relative or absolute risk reduction for a decrease in the incidence (decrease in the proportion of preterm birth <37 weeks).
Table S5. Details on minimal important differences used for power calculations expressed as absolute difference in ordinal or continuous outcome variables
Table S6. List of surrogate outcomes.