Table 2

Risk of bias assessment in included studies

EPOC criteria for randomised controlled trials and controlled before-and-after studies
Study NoReferenceAdequate sequence generationAdequate concealment of allocationSimilar baseline outcome measuresSimilar baseline characteristicsAdequate follow-upBlinding of outcome measuresAdequate protection against contaminationFree from selective outcome reportingFree from other risks of bias
1Chambliss et al23?+?+++++
2Law and Lam24++?++++++
3Bernitz et al25,26++?++++++
4Hofmeyr et al27??+++++
Newcastle-Ottawa Scale and STROBE quality assessment tool for cohort studies
Study NoReferenceRepresentativeness*Selection of the controls*Ascertainment of exposure*Outcomes not present at the start*Comparability for parity*Assessment of outcome*Follow-up duration*Adequate follow-up*All outcome measures reported†Authors discuss sources of bias†
5Homer et al28++++++++
6Rana et al29+++++++++
7Eide et al30+++?NA?+++
8Suzuki et al31, Suzuki32+++++++++
9Cheung et al33 34+++++++
10Brocklehurst et al35; Schroeder et al36++++++++++
  • +, low risk of bias; −, high risk of bias; ?, unclear risk of bias.

  • *Newcastle-Ottawa Scale.

  • †STROBE quality assessment tool.

  • ‡Eide et al30 only recruited nulliparous women.

  • EPOC, Effective Practice and Organisation of Care group; NA, not applicable; STROBE, Strengthening the Reporting of Observational Studies in Epidemiology.