CRD Summary: This review assessed the effectiveness of progesterone on the occurrence of delivery or intrauterine death before 34 weeks of gestation in women with twin pregnancy, concluding that progesterone was not effective. Despite the relatively limited literature search and poor reporting of some aspects of the review, the authors' conclusions appear to reflect the evidence and are probably reliable.

CRD Commentary: The review question was clear and was supported by appropriate inclusion criteria. However, the literature search was limited to two databases and limited to published studies, which means that potentially relevant articles may have been missed. The authors reported some detail on the review process to reduce reviewer error and bias. There may also have been some selection bias, as the authors included their own RCT in the review. A reliable scale (Jadad) was used to assess validity on the studies identified from the literature search; the studies were of the highest quality. There was no evidence of statistical heterogeneity, so pooling of the results seemed appropriate. However, patient and study details for the included studies were very limited. It was unclear whether clinical and methodological heterogeneity may have been present. Despite the relatively limited literature search and poor reporting of some aspects of the review, the authors' conclusions appear to reflect the evidence and are probably reliable.