Fig. 2From: Association between maternal sleep duration and quality, and the risk of preterm birth: a systematic review and meta-analysis of observational studiesForest plot (random-effects model) of sleep duration (shortest vs. longest) and preterm birth risk. The squares indicate study-specific hazard ratios (size of the square reflects the study-specific statistical weight); the horizontal lines indicate 95% CIs; and the diamond indicates the summary hazard ratio estimate with the related 95% CIs. CI, confidence interval; RR, relative riskBack to article page