Additional file 3: Risk of bias within studies
1) Risk of bias assessment for randomized controlled trials based on the Cochrane
Collaboration’s risk of bias criteria
Extremely preterm birth (RCTs)
1.
Study ID
Type of study
Bias
Sequence generation
Allocation concealment
Blinding of participants and
personnel
Blinding of outcomes
Incomplete outcome data
2.
Support for judgment
High
Not blinded
Unclear
Low
Not mentioned
All patients completed study
All specified outcomes in methods reported following the
standard protocol
Insufficient information to assess other bias exsit
Selective reporting
Low
Other bias
Study ID
Type of study
Unclear
Romero 2000
RCT
Author’s
judgment
Low
Low
Bias
Sequence generation
Allocation concealment
Blinding of participants and
personnel
Blinding of outcomes
Incomplete outcome data
Selective reporting
Other bias
3.
Richter 2005
RCT
Author’s
judgment
Unclear
Unclear
Study ID
Type of study
Bias
Sequence generation
Allocation concealment
Blinding of participants and
personnel
Blinding of outcomes
Incomplete outcome data
Selective reporting
Other bias
Low
Not described
Not described
Support for judgment
Computer-generated randomization
Opaque envelopes
Double blinded
Low
Low
Low
Blinded
Intended to treat; same numbers, same reasons for attrition
Study protocol available and same outcomes reported
Imbalance of baseline characteristics, with younger preterm
Unclear
births allocated to atosiban group
The Canadian Preterm Labor Investigators Group (PLIG) 1992
RCT
Author’s
Support for judgment
judgment
Patients, physicians and nurses blinded to women’s treatment
Low
allocation
Low
Done by pharmacy–controlled randomisation
Low
Double blinded
Low
Unclear
Low
Low
Blinded
Loss to follow-up unclear, not explained in detail
Study protocol available and all expected outcomes reported
The study appears to be free of other sources of bias
2) Risk of bias summary for studies included extremely preterm birth (RCTs)
3) Risk of bias assessment for non-randomized studies based on the Risk of Bias Assessment
tool for Non-randomized Studies’ criteria (RoBANS)
Extremely preterm birth (non-RCTs)
1)
Study ID
Type of study
Bias
2)
Selection of participants
Confounding variables
Measurement of exposure
Blinding of outcomes
Incomplete outcome data
Selective reporting
Study ID
Type of study
Bias
Selection of participants
Confounding variables
Measurement of exposure
3)
Blinding of outcomes
Incomplete outcome data
Selective reporting
Study ID
Type of study
Bias
Selection of participants
4)
Confounding variables
Measurement of exposure
Blinding of outcomes
Incomplete outcome data
Selective reporting
Study ID
Type of study
Bias
Selection of participants
Confounding variables
Measurement of exposure
Blinding of outcomes
Incomplete outcome data
Selective reporting
Berghella 2009
Retrospective cohorts
Author’s
Support for judgment
judgment
Low
All women with high risk preterm select from medical database
Low
Confounding variables adjusted by multivariable regression
Low
Medical examination
Low
Not blinded, but outcome most likely not influenced
Unclear
The number of excluded or missing data were not described
Low
Results correspond to intended estimate outcomes reported
Cape 2010
Retrospective cohorts
Author’s
Support for judgment
judgment
Unclear
Population’s origin not described
Low
Adjusted through Cox regression
Although source is unclear, information was only found in
Unclear
medical records
Low
Not blinded, but outcome most likely not influenced
Unclear
Not mentioned clearly
Unclear
Abstract report contained too few information
Manuck 2012
Retrospective cohort
Author’s
Support for judgment
judgment
All women with high risk preterm select from a single
Low
healthcare system database
High
Not adjusted
Low
Medical records
Low
Not blinded, but outcome most likely not influenced
Unclear
Not mentioned
Unclear
Abstract report contained too few information
Visintine 2008
Retrospective cohort
Author’s
Support for judgment
judgment
All women in the study have same risk and in same University
Low
database
Low
Confounding variables adjusted by logistic regression
Low
Medical records
Low
Not blinded, but outcome most likely not influenced
Low
Identified data and loss to follow-up described
High
Side effects and adverse outcomes not assessed
4) Risk of bias summary for studies included extremely preterm birth (non-RCTs)