My mother used DES while she was pregnant with me. Does this use of DES in utero increase the risk of endometriosis?

No, but.... This is a tough question. First of all, the use of des was a long time ago. How old are you? It is unlikely that reproductive age women were exposed to des. Des did cause uterine abnormalities, but i don't know of any evidence that it increased the risk of endometriosis.