According to the National Institutes of Health, evening primrose oil is high in prostaglandins and contains gamma-linolenic acid, a type of omega-6 fatty acid. Prostaglandins soften the cervix so that it is ripe to begin dilation and effacement as labour progresses; they are naturally produced in higher amounts by the body in preparation for labour and delivery. The use of evening primrose oil to start labour has been around for a long time, and many midwives swear by this technique when helping pregnant patients prepare for delivery. Evening primrose oil does not directly trigger the start of labour, but works by softening and ripening the cervix. This allows the baby's head to engage in the pelvis, encouraging dilation. Not everyone agrees that evening primrose oil will help to soften the cervix.
Visit your obstetrician for permission to use evening primrose oil to start labour, and to make certain your membranes are intact. The introduction of any substance into the vagina, or through the cervix, after a tear or rupture in your membranes may result in a serious infection that could put you and your baby at risk.
Take two 500 mg capsules of evening primrose daily, as soon as 36 weeks' gestation. This will help slowly ripen and soften your cervix, but will not cause you to go into preterm labour.
Increase the amount of capsules you are taking each day to three or four when you reach 38 weeks' gestation. Decrease your dose if you experience nausea or diarrhoea, which are two common side effects of evening primrose oil.
Insert a capsule into your vagina before bed each night throughout the last few weeks of your pregnancy. This should be done immediately before bed, as your body heat will dissolve the capsule and the oil will leak out of your vagina if you walk around.
Use evening primrose oil as part of a perineal massage. Have your partner help you with this, if possible. Numerous studies, including one published in the American Journal of Obstetrics and Gynecology, show that daily massage of the perineum during the last month of pregnancy reduces the likelihood that an episiotomy will be needed during delivery.
Using evening primrose oil is not widely accepted in the medical community.
A study published in the May 1999 issue of the Journal of Nurse-Midwifery failed to show a shortening of gestation or a decrease in labour length in women who consumed oral evening primrose oil from the 37th week until birth. Do not take evening primrose oil before the 36th week of gestation.