Supplementary Material for: Chorioamnionitis as a Risk Factor for Retinopathy of Prematurity: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> The role of chorioamnionitis (CA) in the development of retinopathy of prematurity (ROP) has not been well established. <b><i>Objective:</i></b> To conduct a systematic review and meta-analysis of the association between CA and ROP in preterm infants. <b><i>Data Sources:</i></b> The authors searched MEDLINE, Embase, CINAHL, Cochrane Central Register of Controlled Trials and PubMed, reviewed reference lists of relevant articles, abstracts and conference proceedings (Society for Pediatric Research, European Society for Paediatric Research 1990-2012), sought results of unpublished trials, and contacted the primary authors of relevant studies. <b><i>Study Selection:</i></b> Studies were included if they had a comparison group, examined preterm infants, and reported primary data that could be used to measure the association between exposure to CA and the development of ROP. <b><i>Data Extraction:</i></b> Two reviewers independently screened the search results, applied inclusion criteria and assessed methodological quality using the Newcastle-Ottawa Scale. One reviewer extracted data and a second reviewer checked data extraction. Summary relative risks (RRs) were calculated using a random effects model. <b><i>Data Synthesis:</i></b> We identified 1,249 potentially relevant studies from the electronic databases. Twenty-seven studies involving 10,590 preterm neonates with 2,562 cases of ROP were included. Taking into account all included studies without adjusting for gestational age (GA), CA was significantly associated with ROP (any stage) [summary RR 1.33 (95% CI 1.14-1.55, I<sup>2</sup> = 77%, p<sub>heterogeneity</sub> < 0.0001)], and a borderline significant association was observed for severe ROP (stage ≥3) [summary RR 1.27 (95% CI 0.99-1.63, I<sup>2</sup> = 74%, p<sub>heterogeneity</sub> < 0.0001)]. There was no publication bias with Begg's test. However, subgroup analysis of studies adjusting for GA showed no significant association on CA with ROP [summary RR 0.98 (95% CI 0.77-1.26, I<sup>2</sup> = 0%, p<sub>heterogeneity</sub> = 0.89)]. <b><i>Conclusion:</i></b> Unadjusted analyses showed that CA was significantly associated with ROP (any stage) as well as with severe ROP (stage ≥ 3). However, the association disappeared on analysis of studies adjusting for GA. Hence, CA cannot be definitively considered as a risk factor for ROP, and further studies should adjust for potential confounding factors and report results by stage to clarify the association with severe ROP.