Clinical trials registries are underused in the pregnancy and childbirth literature: a systematic review of the top 20 journals.

Background: Systematic reviews and meta-analyses that do not include unpublished data in their analyses may be prone to publication bias, which in some cases has been shown to have deleterious consequences on determining the efficacy of interventions.

Methods: We retrieved systematic reviews and meta-analyses published in the past 8 years (January 1, 2007-December 31, 2015) from the top 20 journals in the Pregnancy and Childbirth literature, as rated by Google Scholar's h5-index. A meta-epidemiologic analysis was performed to determine the frequency with which authors searched clinical trials registries for unpublished data.