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In this episode, I cover the evidence on evening primrose oil (EPO) for natural labor induction. This oil is extracted from the seed of the evening primrose plant, which grows wild in North America and some parts of Europe. It’s a rich source of omega six essential fatty acids, as well as other compounds which are thought to help ripen the cervix for labor. 

I share the results of randomized control trials for administering EPO vaginally and taking it orally, as well as observational studies, a case report, and studies looking at EPO for cervcial ripening for non-pregnancy gynecological procedures. 

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  • Aquino, P. A., Fernandez, H. D., Garcia, M. I., et al. (2011). Determining the Ease of Cervical Dilation in Patients Given Evening Primrose Oil (Eveprim®) Intravaginally before Hysteroscopy in Postmenopausal and Nulliparous, Premenopausal Women Ages 37-77 Years Old: A Pilot Study. [Abstract Only]. Click here.

  • Diansuy, N. N. and Aguilar, A. S. (2017). The effectiveness of evening primrose oil gel capsule as a cervical ripening agent during labor induction as measured by bishop score on term singleton pregnant patients. Philippine Journal of Obstetrics and Gynecology. Volume 41(2), 1-4. Click here. Free full text!

  • Dove, D., & Johnson, P. (1999). Oral evening primrose oil: its effect on length of pregnancy and selected intrapartum outcomes in low-risk nulliparous women. J Nurse Midwifery, 44(3), 320-324. Click here.

  •  Kalati, M., Kashanian, M., Jahdi, F., et al. (2018). Evening primrose oil and labour, is it effective? A randomised clinical trial. J Obstet Gynaecol. 38(4), 488 -492. Click here.

  • Mahboubi, M. (2019). Evening Primrose (Oenothera biennis) Oil in Management of Female Ailments. J Menopausal Med. 25(2), 74-82. Click here. Free full text!

  • Najafi, M., Loripoor, M., Saghafi, Z., et al. (2019). The effect of vaginal evening primrose on the Bishop score of term nulliparous women. NPT. 6(4), 202-211. Click here. Free full text!

  • Shahali, S., Khatami, F., Abbaspoor, Z., et al. (2018) The effect of vaginal evening primrose capsule on cervical ripening in nulliparous women with post-term pregnancy: A clinical trial. The Iranian Journal of Obstetrics, Gynecology and Infertility, 21 (8), 30-38. [English Abstract Only]. Click here.

  • Tanchoco, M. and Aguilar, A. S. (2015). Cervical priming prior to operative hys- teroscopy: a randomized controlled study comparing the efficacy of laminaria versus evening primrose oil (EPO). J Minim Invasive Gynecol. 22(6S): S45. [Abstract only]. Click here.

  • Ty-Torredes, K. A. (2006). The effect of oral evening primrose oil on bishop score and cervical length among term gravidas. American Journal of Obstetrics and Gynecology, 195(6), S30. Click here.

  • Vahdat, M., Tahermanesh, K., Mehdizadeh Kashi, A., et al. (2015). Evening Primrose Oil Effect on the Ease of Cervical Ripening and Dilatation Before Operative Hysteroscopy, Thrita. 4(3), e29876. Click here. Free full text!

  • Verano, R. M. A and Veloso-Borromeo, M. G. (2015). The efficacy of evening primrose oil as a cervical ripening agent for gynecologic procedures: A single-blinded, randomized controlled trial. Philippine Journal of Obstetrics and Gynecology. 39(1), 25-8. Click here. Free full text!

  • Wedig, K. E., & Whitsett, J. A. (2008). Down the primrose path: petechiae in a neonate exposed to herbal remedy for parturition. J Pediatr, 152(1), 140, 140.e141. Click here.



Hi everyone. On today’s podcast, we’re going to talk about evening primrose oil for natural labor induction.

Welcome to the Evidence Based Birth Podcast. My name is Rebecca Dekker and I’m a nurse with my PhD and the founder of Evidence Based Birth. Join me each week as we work together to get evidence based information into the hands of families and professionals around the world. As a reminder, this information is not medical advice. See for more details.

Hi everyone, I am excited to welcome you to this episode of the Evidence Based Birth Podcast. In this episode, we’re going to be featuring the evidence on another natural labor induction technique. We’ve already covered the evidence on acupuncture and acupressure, nipple stimulation, castor oil and eating date fruit in prior episodes of the podcast.

Today, we’re going to move on to the alphabet and talk about evening primrose oil or EPO for natural labor induction. Evening primrose oil is extracted from the seeds of the evening primrose plant. Evening primrose plant, is a plant with yellow flowers that grows wild in North America and some parts of Europe. The oil from this plant is a rich source of Omega six essential fatty acids, and it contains about 70% linoleic acid and seven to 10% gamma linolenic acid.

Gamma linolenic acid is thought to be the active ingredient in EPO. It is a precursor of prostoglandins E1 and E2 and these are prostoglandins that help ripen the cervix and ready the cervix for labor. So researchers have speculated that EPO impact on prostate glandons could benefit cervical ripening and natural labor induction.

In this podcast, I’m going to share with you the results from two randomized control trials that looked at the effects of administering EPO vaginally, two randomized control trials that looked at the effects of taking it orally by mouth. I’ll also share with you the results of several observational studies, a case report and studies looking at EPO for cervical ripening in people who are not pregnant, but are going in for gynecological procedures.

There is a lot of new research on evening Primrose oil since the last time we talked about this on our YouTube video in 2017. In fact, just last year in 2019, researchers published the first randomized control trial to evaluate the effects of vaginal EPO on cervical ripening of first time mothers at term. This study was published by Najafi et al, and it was conducted in Iran. The study was double blinded. So neither the participants, nor the investigator knew who received EPO and who got a placebo.

86 first time mothers participated in the study. 43 people were randomly assigned to each group. Everyone was between 18 and 35 years old. They were 38 weeks pregnant. They were pregnant with just a single baby. They were not having any contractions, and they had an intact amniotic sac.

In order to be in the study. Mothers could not have any chronic health conditions. They could not have had a prior Syrian or other uterine surgery. And they had to have no known history of substance abuse. They also excluded anyone with an allergy to the capsule, anyone with pregnancy complications and anyone who was using other methods to facilitate vaginal birth, including having sex, taking laxatives or other herbal capsules.

The intervention group was the EPO group or evening promos oil group. They received a daily dose of 1000 milligrams of EPO in a soft vaginal capsule starting with the 38th week of pregnancy until birth. The placebo group received an identical placebo containing paraffin to use in the same way. Everyone was instructed to insert a vaginal capsule every night and to remain lying down for at least two hours after inserting the capsule if possible. Participants kept a daily recording form and received phone calls from the researcher every 48 to 72 hours.

The researchers found a significant difference in the average Bishop’s score at the time of admission for birth between the two groups. We’ve talked about the Bishop score in prior podcast episodes, the Bishop score is the most commonly used method to rate the readiness of the cervix for labor. It measures dilation, effacement or thinning of the cervix, where the baby’s station is in relation to your pelvis, the consistency of your cervix, and the position of your cervix.

A Bishop score of eight or greater is considered to be favorable for someone who’s about to be induced. A score of six or less is considered to be unfavorable for an induction.

In this randomized trial, the Bishop’s score was an average of 7.83 with EPO, versus 4.46 with the placebo. All five criteria of the Bishop’s score, including cervical dilation and effacement position and consistency and fetal descent were all significantly improved in the intervention group compared to the placebo group. The EPO group also had a shorter average length of early labor, four to five hours, versus eight to nine hours. There were fewer cesarean in the EPO group, 21% versus 47%, and less use of synthetic oxytocin to induce labor. 29% versus 62%.

There were no differences between groups in the length of active labor or the length of the second stage of labor, the use of Pitocin to augment labor, the baby’s Apgar scores at one in five minutes, the amount of synthetic oxytocin used after the birth and the rate of postpartum hemorrhage. No side effects were reported.

The authors concluded that in this study, vaginal use of EPO with a daily dose of 1000 milligrams from the 38th week of pregnancy until birth can be used to ripen the cervix of first time birthers at term, and can be used clinically for this purpose. They said, “according to the results of the present study, vaginal capsules of evening Primrose oil could be an effective, safe, affordable, and without the necessity of being hospitalized, method to achieve cervical ripening in term NOI Paris women. More studies in this field are required.”

So that’s the only study we have on vaginal use of EPO. And it was a relatively small study, with only 86 people. So we do need more research on that topic.

Another recent randomized control trial from Iran evaluated the effects of vaginal EPO on cervical ripening in first-time birthers who had a post-term pregnancy. This study was published by Shahali in 2018. Unfortunately, only the abstract of this study is available in English. So we could not evaluate the full text of the study.

The participants in the study included 60 pregnant people who had a post-term pregnancy. The groups were randomly assigned either a single vaginal capsule of 1000 milligrams EPO, or a placebo vaginal capsule that contained gelatin. Both groups received induction of labor with 10 units of synthetic oxytocin and 1000 milliliters of fluid for the IV drip, along with their vaginal capsules. Cervical ripening was measured every hour after the intervention.

The researchers has found that the length of the early phase of labor and the average Bishop score were both significantly improved among the people assigned EPO with their inductions. There were no differences between the two groups in terms of the length of active labor, pain scores or blood loss. The authors concluded that vaginal use of 1000 milligrams EPO alongside a medical labor induction reduces the length of early labor and has a positive effect on cervical ripening and the Bishop score.

Next, let’s look at the randomized control trials on the effects of oral EPO, or taking evening promotes oil by mouth. In 2018. Kolodny et al, published a randomized control trial from Iran, that looked at the effects of oral EPO on the length of pregnancy and labor. This study was conducted as a triple blind placebo controlled randomized clinical trial, meaning that the participants and the investigator were not aware of which capsules were EPO, and which were placebo. And the statistician who performed this statistical analysis was also not aware of the group assignments.

The study participants were first time mothers who had reached 40 completed weeks of pregnancy with single headfirst babies. They all had to have Bishops scores of less than four, an estimated fetal weight between 2500 and 4,000 grams, a BMI between 19 and 25 and normal ultrasound and biophysical profiles. They excluded people with any conditions that made the pregnancy higher risk.

The EPO group had 40 people, and they received 1000 milligrams of EPO orally twice daily for seven days. But placebo group also had 40 people and they received their placebo capsule the same way. It was similar to the EPO capsule in taste, smell, shape, and color.

The findings of this study were that there were no difference between the two groups in gestational age at birth, improvement in Bishop score, need for induction or augmentation of labor or the length of different stages of labor. No side effects were noted in either group.

The authors concluded that there is not enough evidence to show that EPO is effective for cervical ripening or for natural labor induction or augmentation. They suggest that the use of EPO in pregnancy should be limited to randomized control trials, and that future trials should study different routes and different dosages.

So why is it that these researchers found negative results? They didn’t find any benefit from the EPO when the prior randomized control trials that I just talked about did find beneficial effects. It’s likely due to the method of administration. In this study, they administered the EPO orally and in the two successful randomized trials, it was administered vaginally. So it may be that vaginal EPO is more effective. It could also be that the duration of using EPO in this study wasn’t enough. It was only for one week, starting at 40 completed weeks of pregnancy.

In addition, some of the people did not use their full dosage of EPO that they were prescribed. Only 28% of people in the EPO group completed 14 capsules. And half of the people in the EPO group used their capsules for less than five days.

In the study by Najafi et al in 2019, where they found a positive effect on cervical ripening with vaginal EPO, participants in that study used a 1000 milligram vaginal EPO capsule daily starting from the 38th week of pregnancy until birth.

There was an earlier randomized controlled trial from the Philippines that was published by Thai Tardies in 2006. They included a total of 71 subjects assigned to either oral EPO or placebo. Unfortunately, only the abstract or summary is available for the study.

This was a randomized double blind placebo controlled study. Participants received one 500 milligram capsule given orally three times daily for one week. So they had a total of 1500 milligrams per day by mouth. To be included in the study, everyone was healthy, at term, with no pregnancy complications. The researchers reported that the EPO group saw significant improvement in Bishop score and a significant reduction in cervical length compared to the placebo group. The effect was greater among first-time birthers and those beyond 39 weeks of pregnancy. There was no difference between groups with regards to the interval, from treatment to the onset of labor or the use of synthetic oxytocin. More people in the EPO group gave birth vaginally. 70% versus 51%. And there was no effect on fetal safety monitored by modified biophysical profiles and non-stress tests. Again, unfortunately, because we only have the abstract of this study, we can’t get more detailed info about that study.

In 2017, Dan Swe and Aguilar published an observational study from the Philippines where they measure the effectiveness of vaginal EPO as a cervical ripening agent with people who are pregnant at term. There were 13 participants in this study. They were admitted for a labor induction with an average gestational age of 40 weeks and one day. Some were being induced for medical reasons and others were being induced because they were reaching 41 weeks of pregnancy. They measured the Bishop score four hours before and four hours after inserting six vaginal capsules of 500 milligrams of EPO.

The researchers found a significant change in average Bishop score from baseline to four hours after the insertion of EPO capsules. 11 of the 13 participants had a significant improvement in their Bishop score, four hours after the intervention. Four people improve their Bishop score by four or more points considered clinically significant. When they looked at the individual components of the Bishop score, they saw a significant improvement in dilation, effacement and consistency, but not in the position of the cervix or the station of the baby. There was a very high caesarian rate in this study, of 69%, and 46% of the Syrians were for non reassuring fetal status. However, there was no comparison group of people who did not receive EPO, and many of the participants had health conditions that put them at higher risk for caesarian to begin with, such as diabetes and preeclampsia. So it’s not possible to determine a link between EPO use and cesarean in this study.

In 1999, Devin Johnson published an observational study on EPO that looked retrospectively or backward in time at a sample of people who received care in a freestanding birth center in the US. In this study, 54 low-risk first-time birthing people took oral EPO during pregnancy. They took 500 milligrams, three times a day, starting at 37 weeks for the first week of treatment, followed by 500 milligrams once a day, until labor began. And they compared them with 54 participants who had no treatment. The researchers found no difference between groups in the length of pregnancy or the length of labor. They found longer labors by three hours on average in the group that took EPO. There was also a trend towards more labor complications in the group that took EPO, including more prolonged rupture of membranes, Pitocin augmentation, arrest of descent and vacuum extraction. However, babies in the EPO group ended up being significantly larger than the babies in the control group, and this difference could have affected the outcomes. Another limitation of this study is that there was no strict procedure for defining when labor started.

In 2008, researchers reported a case report of a newborn who experienced skin problems, little bruises after being born to a mother who took raspberry leaf tea and a total of 13, 500 milligram capsules of EPO vaginally and orally in hopes of ripening her cervix to improve labor during the week before giving birth. The infant was otherwise healthy, and the problem resolved by five days of age. That was the only case report we could find on any negative effects.

Now, several studies have evaluated the effects of vaginal EPO on cervical ripening in people who are not pregnant, but they were going in for invasive gynecological procedures.

In 2015, Wada et al, evaluated the effects of EPO on cervical ripening in dilation before an operative hysteroscopy. This study took place in Iran. A hysteroscopy is an operative procedure where the provider inserts a thin tube through the closed cervix to examine the cervix in the inside of the uterus, in order to diagnose or treat problems such as infertility or abnormal bleeding. Priming agents, including prostoglandins are used to ripen the cervix before the procedure.

In this study, the researchers randomly assigned 28 people to receive two soft gels of EPO, 500 milligrams each, and 22 people to receive a placebo. In both cases, the soft gels were applied to the far back of the vagina, six to eight hours before the procedure. They found the EPO is effective at ripening the cervix before the procedure. It was easy to use, available, inexpensive and had no side effects.

Three other studies from the Philippines have also found improved cervical dilation with high doses that they did not define, a vaginal EPO given in the eight hours before gynecologic procedures. Ovno, one of the studies mentioned puncturing the capsules before inserting them vaginally. There were no bad side effects noted in any of the studies. Those studies had a total of eight people, 80 people and 84 people.

So in summary, there has been a lot of new research, especially coming out in the past couple of years on using EPO for cervical ripening. So far, the studies show that EPO may have some therapeutic potential for cervical ripening. In all, we found four randomized control trials on using EPO for cervical ripening. Two of the trials looked at vaginal use, and two of them looked at oral. Use both of the trials on vaginal use of EPO found that it was useful for cervical ripening among people giving birth for the first time.

One of the studies used a daily dose of a thousand milligrams inserted vaginally, starting at the 38th week of pregnancy until birth. And the other study used a onetime dose of 1000 milligrams alongside a medical labor induction for post-term pregnancy.

Of the two studies on oral use of EPO, one found benefits for cervical ripening using one 500 milligram capsule, three times daily for one week. The benefits were most pronounced among first time parents and those beyond 39 weeks of pregnancy. The other randomized control trial on oral use of EPO among first time mothers, a thousand milligrams given twice daily for seven days, starting at 40 weeks found that oral EPO made no difference in cervical ripening, the length of pregnancy or the length of labor. No bad side effects were reported in any of these studies.

Our recent review article cautioned that EPO should be avoided in people with schizophrenia and other psychotic disorders who take phenothiazine, a medication. And that EPO may raise the risk of bleeding among people who take anti-platelet and anticoagulant drugs. In addition, some people have complained of nausea, headache, and diarrhea after using EPO.

The case report of a newborn who experienced skin lesions after maternal use of EPO is troubling, but we can’t be certain that the EPO caused the newborn’s condition. It’s definitely best practice to talk with your care provider before taking EPO or any other supplement. Also, keep in mind that the people in these studies were all healthy, with no pregnancy complications. Also, most of these studies excluded people who were going for a vaginal birth after cesarean. So we have no safety data on taking EPO if you’re planning a VBAC.

After looking at the evidence, it seems like there may be some promise with the use of vaginal EPO, less so for the oral EPO. At this time, there are differing opinions in the research about whether EPO should be used clinically for cervical ripening, or if it’s use during pregnancy should be limited to people who are enrolled in clinical trials. Although there are four randomized trials on this topic, they’re all fairly small, and so we can’t rule out that there might be other adverse effects related to using EPO to ripen the cervix.

If you’d like to look at the research for yourself, make sure to check out the blog article that goes with this podcast, where we linked to all the references for the scientific studies we have mentioned in this podcast. Thanks for listening. I hope you learned something new and I’ll see you next week. Bye.

Today’s podcast was brought to you by the comfort measures for labor and delivery nurses workshop. Last year at Evidence Based Birth, we hosted focus groups and talked with nurses from across the US, who told us that they wish they had a way to learn or refresh their comfort measure skills to use with birthing clients. So we created the comfort measures for labor and delivery nurses workshop. This is a three hour in-person workshop with nursing contact hours. If you’re a nurse, midwife or doula who wants hands on practice with massage, acupressure, upright birthing positions, and more, visit to find a workshop near you.

Listening to this podcast is an Australian College of Midwives CPD Recognised Activity.

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