I know of a few midwives who have used it. It does work but it takes therapeutic levels like you were treating an acute infection. As Pam said it is endangered, and I don't recommend its use. As unpleasant as it may seem to some people probably one of the oldest plant medicines still in use castor oil will usually work, and is safe. If it doesn't work it will usually clean out the colon and for many pregnant women this is a relief. With all the newer testing we now know that not only does it work as an indirect irritant to but also it works through elevating prostaglandins. Even if you don't start labor it will have prepared the body a bit more by raising the prostaglandin levels. This is also how goldenseal would work it is a mucous membrane irritant-but unlike castor oil it can also have an effect on the placental bed partly because it is a very strong astringent, and partly because it is absorbed systemically, where as most of the bits of castor oil are "local" irritants and don't absorb as much systemically.