Here is a reference to a small study demonstrating that yoga helps menstrual pain by lowering homocysteine levels. My own personal experience is that yoga has helped me in dealing with my endometriosis/chronic pelvic pain; and both my doctor and pelvic physical therapist recommend that I continue with it. It doesn't always take the pain away, but I think overall it lessens it, lessens the reaction my body has to pain, and helps me feel better mentally and emotionally too.
"More recent research has reported on the potential scientific relationship between yoga and easing of menstrual symptoms. During menstruation, women who have painful periods have been observed to have higher serum levels of nitric oxide (NO), homocysteine, and other factors related to possible endothelial dysfunction. Research by Chien and colleagues assessed such blood serum levels for such markers in 30 women with dysmenorrhea and in 30 controls. Participants were instructed in yoga therapy 2x/week for 8 weeks, and each session was 30 minutes in length. The study concludes that yoga intervention can reduce severity of dysmenorrhea and may be effective in reducing serum homocysteine levels." http://hermanwallace.com/blog?start=30 "In the study by Rakhshaee, 92 female students (ages 18-22) were randomly assigned to a treatment group (n=50) and to a control group (n=42). Over a period of 3 menstrual cycles, participants recorded pain using a Visual Analog Scale and reported pain duration in terms of hours. During the first menstrual cycle, symptoms were recorded, and then during the second and third cycles, the treatment group was asked to complete 3 yoga poses during the luteal phase. The control group received no intervention. Yoga poses instructed include the Cat, Fish, and Cobra.
"In the experimental group, both the pain intensity and the pain duration showed significant differences with the participants who completed yoga poses having less pain intensity and pain duration. The authors conclude that yoga is a safe and simple treatment for primary dysmenorrhea. Oftentimes, patients who complain of dysmenorrhea lack access to care for this other than medications that might include pain medication or birth control pills. Instructing a patient in basic yoga postures presented in this research may be a simple alternative to such medications. There are several websites that offer free access not only to images of poses, but also to free classes. I often hear from patients that they enjoy taking advantage of free fitness classes including yoga on various television stations. This may be another "tool in the toolbox" that we can offer to patients who have pain related to the menstrual cycle." http://hermanwallace.com/blog/yoga-for-menstrual-pain.html
From Yoga Journal, poses for endometriosis: http://www.yogajournal.com/practice/686 (they do mention retrograde menstruation once but in this article http://www.yogajournal.com/practice/1187 they say "One study, however, found that retrograde menstruation naturally occurs in 90 percent of women, most of whom never develop endometriosis. So we do not know for sure if inversions increase retrograde flow or whether the backward flow increases the risk of endometriosis.")
Yoga for Endometriosis and Pelvic Pain: http://www.endoyoga.com/
YinYoga Video for endo: http://www.yogayin.com/yoga-for-endometriosis-part-one-video-blog/
Older blog post about stretches/yoga to help with pelvic pain: http://endocomprehensive.blogspot.com/2013/11/some-stretches-to-help-pelvic-pain.html
Yoga for Pelvic Pain DVD: http://yourpaceyoga.com/yoga/
