Mandana Mansour Ghanaei - Reproductive Health Research Center, Department of Obstetrics and Gynecology, Alzahra Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.
Maryam Asgharnia - Mehr Fertility Research Center, Guilan University of Medical Sciences, Rasht, Iran.
Maryam Farokhfar - Reproductive Health Research Center, Department of Obstetrics and Gynecology, Alzahra Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.
Seyed Mohammah Asghari Ghalebin - Reproductive Health Research Center, Department of Obstetrics and Gynecology, Alzahra Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.
Elahe Rafie - Razi Clinical Research Development Unit, Guilan University of Medical Science, Rasht, Iran.
Katayoun Haryalchi - Reproductive Health Research Center, Department of Obstetrics and Gynecology, Alzahra Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.

Background: Herbal medicine could be effective at treating various illnesses. Hysteroscopy can be as an effective method for assessing the uterus in terms of anatomical, physiological and pathological anomalies. Objective: This study aims to evaluate the effect of evening primrose oil (EPO) on cervical preparation in women candidates for hysteroscopy. Materials and Methods: This study was a double-blind, randomized controlled clinical trial including ۱۶۰ women candidates for diagnostic hysteroscopy who were referred to Al-zahra hospital from August ۲۰۱۹-March ۲۰۲۰. They were divided in ۲ groups. Group A received ۱۰۰ mg EPO as a soft gel capsule ۶ hr before the hysterectomy in the posterior vaginal fornix. Group B received a placebo. After receiving the treatment, primary and secondary outcomes were evaluated in gropus. Results: The average Hegar size in the EPO group was larger than in the control group (p < ۰.۰۰۱, for both). Also, the need for mechanical dilation, the time taken until the first resistance and the time of dilatation completion in the EPO group were significantly less than in the placebo group (p < ۰.۰۰۸ for all). There was also greater ease of dilatation in the EPO group. Side effects such as uterine rupture, false passage, cervical rupture, allergic reaction, abdominal pain, nausea, diarrhea, headache and increase of bowel movements were not reported in any cases. Conclusion: Based on the findings of the present study, EPO is effective for cervical preparation in women undergoing hysteroscopy.

Hysteroscopy, Dilatation, EPOGAM, Gamma-linolenic acid.