Association between maternal sleep duration and quality, and the risk of preterm birth: a systematic review and meta-analysis of observational studies

Table 4 Methodological quality of observational studies included in the meta-analysis

First author, (Ref), year	Selection				Comparability	Outcome
Cohort study	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow up of cohorts
Trivedi et al., [30] 2018	☑	☑	☑	☑	–	☑	☑	☑
Li et al., [31] 2017	☑	☑	☑	☑	☑	☑	☑	☑
Ota et al., [35] 2017	☑	☑	☑	☑	☑	☑	☑	☑
Blair et al., [36] 2015	☑	☑	☑	☑	☑	☑	☑	☑
Guendelman et al., [12] 2013	☑	☑	☑	☑	☑	☑	☑	☑
Okun et al., [33] 2012	☑	☑	☑	☑	☑☑	☑	☑	☑
Reutrakul et al., [34] 2011	☑	☑	☑	☑	☑	☑	☑	☑
Okun et al., [14] 2011	☑	☑	☑	☑	☑	☑	☑	☑
Micheli et al., [13] 2011	☑	☑	☑	☑	☑☑	☑	☑	☑
First author, (Ref), year	Selection				Comparability	Exposure
Case-control study	Is the case definition adequate	Representativeness of the cases	Selection of Controls	Definition of Controls	Comparability of cases and controls on the basis of the design or analysis	Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-Response rate
Kajeepeta et al., [32] 2014	☑	☑	☑	☑	☑☑	☑	☑	☑

The risk of bias of all studies included in this meta-analysis was based on the Newcastle–Ottawa quality assessment scale
The definition/explanation of each column of the Newcastle–Ottawa Scale is available at http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp

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