Fig 1.
Flow-chart of study selection.
Table 1.
Characteristics of studies included in the meta-analysis.
Table 2.
Methodological quality of cohort studies included in the meta-analysis*.
Table 3.
Methodological quality of case-control studies included in the meta-analysis*.
Table 4.
Methodological quality of cross-sectional studies included in the meta-analysis*.
Fig 2.
Forest plots (random effect model) of meta-analysis on the relationship between passive maternal smoking and preterm birth by study design.
Squares indicate study-specific risk estimates (size of the square reflects the study-specific statistical weight); horizontal lines indicate 95% CIs; diamond indicates the summary risk estimate with its 95% CI.
Fig 3.
Funnel plot corresponding to the random-effects meta-analysis of the relationship between passive maternal smoking and preterm birth.
Fig 4.
Forest plots (random effect model) of meta-analysis on the relationship between passive maternal smoking and preterm birth by exposure location.
Squares indicate study-specific risk estimates (size of the square reflects the study-specific statistical weight); horizontal lines indicate 95% CIs; diamond indicates the summary risk estimate with its 95% CI.
Table 5.
Summary risk estimates of the associations between passive maternal smoking and preterm birth.
Fig 5.
Sensitivity plot corresponding to the relationship between passive maternal smoking and preterm birth.