I've never tried this, but apparently sage decreases blood estrogen levels. (birthwithoutfearblog.com)
So the more weight that a woman gains, the higher blood estrogen levels become. (consumerhealthdigest.com)
During pregnancy, the elevated blood estrogen level induces the proliferation of mammary epithelial cells, leading to the development of the mammary gland in preparation for lactation. (sciencedaily.com)