The effect of evening primrose oil on cervical ripening and birth outcomes: A systematic review and meta-analysis

BACKGROUND AND PURPOSE: The results of various studies on the effect of evening primrose oil (EPO) on cervical ripening are controversial. The purpose of this systematic review and meta-analysis was to assess the effect of EPO on cervical ripening and birth outcomes. MATERIALS AND METHODS: The Cochrane Library, Embase, PubMed, Scopus, Web of Science and Persian databases were searched for studies published from the inception of the databases up to February 2021 (search updated in May 2022). Full-text articles published in English or other languages, randomized controlled trials, and quasi experimental studies with control group were included. Studies published in form of conference proceedings, and those whose full texts were not available, as well as studies with control groups receiving other treatments for cervical ripening, and those in which the intervention group received drugs besides EPO were all excluded. The Cochrane handbook was used to determine the risk of bias of the included studies. All data were analyzed using Review Manager 5.4 and reported in forest plots. RESULTS: Seven trials involving 920 women were included in the meta-analysis. In five studies, including 652 participants, cervical ripening was evaluated using Bishop score. The use of EPO was found to significantly improved Bishop score (MD = 3.23; 95% CI: 3.17, 3.29). The meta-analysis showed no significant differences between two comparison groups in terms of 1-min Apgar score and length of the second stage of labor. However, the two groups were significantly different in terms of their 5-min Apgar score and the time interval between administration of EPO and birth. Based on subgroup analysis by route of administration, both vaginal and oral use of EPO increased Bishop score significantly in the intervention group compared to the placebo group. CONCLUSION: This study showed that using EPO in term and post-term pregnant women was clinically effective in improving their Bishop score.