Oral evening primrose oil: its effect on length of pregnancy and selected intrapartum outcomes in low-risk nulliparous women

J Nurse Midwifery. May-Jun 1999;44(3):320-4. doi: 10.1016/s0091-2182(99)00055-5.


Evening primrose oil is widely used by many midwives to hasten cervical ripening in an effort to shorten labor and decrease the incidence of postdates pregnancies. Although its efficacy has been studied in the relief of symptoms of a number of medical conditions, its use has not been well studied, if at all, for the purpose of cervical ripening. The purpose of this study was to investigate the effect of oral evening primrose oil on the length of pregnancy and selected intrapartum outcomes in low-risk nulliparous women. A two group retrospective quasi-experimental design conducted on a sample of women who received care in a birth center, compared selected outcomes of 54 women taking evening primrose oil in their pregnancy with a control group of 54 women who did not. Findings suggest that the oral administration of evening primrose oil from the 37th gestational week until birth does not shorten gestation or decrease the overall length of labor. Further, the use of orally administered evening primrose oil may be associated with an increase in the incidence of prolonged rupture of membranes, oxytocin augmentation, arrest of descent, and vacuum extraction.

MeSH terms

  • Administration, Oral
  • Adult
  • Anti-Inflammatory Agents, Non-Steroidal / administration & dosage
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Cervical Ripening / drug effects
  • Fatty Acids, Essential / administration & dosage
  • Fatty Acids, Essential / pharmacology*
  • Female
  • Humans
  • Labor, Obstetric / drug effects*
  • Linoleic Acids
  • Medical Records
  • Midwifery*
  • Oenothera biennis
  • Plant Extracts / administration & dosage
  • Plant Extracts / pharmacology*
  • Plant Oils
  • Pregnancy / drug effects*
  • Retrospective Studies
  • Treatment Outcome
  • gamma-Linolenic Acid


  • Anti-Inflammatory Agents, Non-Steroidal
  • Fatty Acids, Essential
  • Linoleic Acids
  • Plant Extracts
  • Plant Oils
  • evening primrose oil
  • gamma-Linolenic Acid