It has been stated that "Misoprostol facilitates insertion of an IUD, and reduces the number of difficult and failed attempts of insertions in women with a narrow cervical canal" by Sääv I, Aronsson A, Marions L, Stephansson O, Gemzell-Danielsson K at their article "Cervical priming with sublingual misoprostol prior to insertion of an intrauterine device in nulliparous women: a randomized controlled trial." in Hum Reprod. 2007;22(10):2647. You can reach the article in PubMED