I know this is a very old thread, but I wanted to share my experience with taking Vitex (and conceiving twins), as I think this is a very interesting topic and perhaps my story may be helpful to someone!
I began taking Vitex around Spring of 2012 to help regulate my cycle. I took the tincture, made by Gaia Herbs. We began trying for baby #2 in the fall, and in December I learned I was pregnant. I went to my 8 week ultrasound in February and learned I was pregnant with twins. A total surprise as they do not run in my family (I later from my specialist that contrary to popular belief, twins only run on the mother's side. For example, if your mother and/or grandmother etc have a history of hyperovulation and/or have conceived twins as a result, you have an increased chance of hyperovulating - and conceiving twins - as well).
I was really surprised and in disbelief and began researching what can increase your chance of conceiving twins, and came across an article that mentioned Vitex. I do not know for certain that the Vitex had anything to do with it, but I gave birth to two healthy baby boys the Summer of 2013.
During my pregnancy, I learned from my specialist that anyone can naturally conceive twins, as any woman can ovulate multiple eggs, but she did say that is more common in older women, and I was only 23 at the time of conception.
So I guess I will never know if the Vitex actually played a role in me conceiving twins, but it is interesting nonetheless, and maybe someday there will be actual studies done on this topic!
All the best to you mamas-to-be and those of you TTC! xxx