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Background: Systematic reviews and meta-analyses that do not include unpublished data in their analyses may be prone to publication bias, which in some cases has been shown to have deleterious consequences on determining the efficacy of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analysis was performed to determine the frequency with which authors searched clinical trials registries for unpublished data.

Results: A PubMed search retrieved 372 citations, 297 of which were deemed to be either a systematic review or a meta-analysis and were included for analysis. Twelve (4 %) of these searched at least one WHO-approved clinical trials registry or clinicaltrials.gov.

Conclusion: Systematic reviews and meta-analyses published in pregnancy and childbirth journals do not routinely report searches of clinical trials registries. Including these registries in systematic reviews may be a promising avenue to limit publication bias if registry searches locate unpublished trial data that could be used in the systematic review.