The purpose of the present study was to evaluate the effects of evening primrose oil (EvPO) on the duration of pregnancy and labour. The study was performed as a triple blind placebo controlled randomised clinical trial on nulliparous low-risk women with a certain gestational age of 40 weeks of pregnancy and a Bishop score of less than 4. In the case group (EvPO group), EvPO capsules were administered, 1000 mg, twice daily, for 7 days, and in the control group, placebo was administered similarly. The women of the two groups were followed up to delivery. In total, 80 women finished the study (40 in each group). The women of the two groups did not have significant differences according to age, BMI, Bishop Score at the beginning of the study, gestational age at entering the study, employment status and education level, the number of capsules used and duration of using medications. There was no significant difference between the two groups according to gestational age at delivery, need for induction or augmentation of labour, duration of different stages of labour, neonatal weight and Apgar scores, and the indications for hospital admission. Impact statement What is already known on this subject? Evening primrose oil has been used for the treatment of systemic disorders, which are accompanied with chronic inflammation such as atopic dermatitis, rheumatoid arthritis and psoriasis. Also, it has been proposed for some women's health conditions including breast pain (mastalgia), symptoms of premenstrual syndrome and menopausal symptoms, cervical ripening and induction or augmentation of labour. What do the results of this study add? Evening primrose oil does not have any impact on Bishop Score and the duration of different stages of labour. What are the implications of these findings for clinical practice and/or further research? According to the present study and the other performed studies, there is not enough evidence confirming effectiveness of Evening primrose oil for cervical ripening and duration of labour. It is suggested that pending further data its usage should be limited to experimental RCTs and its use in clinical practice should be prevented. Also, different routes of administration and different dosages should be investigated.
Keywords: Pregnancy; evening primrose oil (EvPO); herbal medicine; labour and delivery; pregnancy outcome.