Here is a thoughtful response from Mary Knauer, CNM. “Evening Primrose Oil contains ingredients that your body can use to produce a hormone called prostaglandin. This hormone is believed to be the precurser to the oxytocin hormone which makes the uterus contract. It is theorized (yes, a guess) that the body will absorb these ingredients and produce prostiglandins earlier causing the cervix to ripen which may (or may not) initiate the production of oxytocin which kicks in the labor. There does not seem to be any harmful effects, so trying it will not increase risks to the pregnancy.

“Let us consider another ‘theory’: That you may have no control over when and where you go into labor….that your body will begin the labor process when all the hormones have naturally come together. Even though you are so uncomfortable right now, it’s possible that your pregnancy could proceed to beyond those 11 days and believing that herbal remedies can possibly shorten the duration can create disappointment and discouragement. Just a theory, but one that I believe to be true. I still suggest the EPO, but never promise it will shorten the pregnancy or the duration of labor. To me, it’s like taking a daily vitamin which the body may–or may not–be able to use.”