Study selection and characteristics
Searches of databases identified a total of 178 studies and manual searches identified one additional publication (Figure 1). Seventy-five papers were removed due to duplication, 46 were excluded on title and abstract review, and an additional 41 were excluded at the level of full text review. Of those excluded at full text screening, 14 were the wrong study design, and two were unable to be sourced. Of the remaining 23: a total of eight did not compare Shirodkar and McDonald, a further 15 did not report usable outcomes that were comparable to the outcomes of interest in this review, and another two reported on the wrong population. This process left a total of 17 studies to be included in the meta-analysis (Figure 1).
A summary of the of key characteristics of the included studies is presented in Table 1. In brief, 17 included studies which consisted of a total of 2063 participants were included in this review; of these, 16 (94.1%) of them were retrospective cohort studies, while one (5.9%) was a multicentre, retrospective study which used data from four randomised control trials. Of the retrospective cohort studies, data were retrieved from women’s records and hospital data collected between 1957 and 2014. The sample sizes for the included studies ranged from 25 to 374 and all studies reported quantitative data.