Brenner P F, Cooper D L, Mishell D R
Am J Obstet Gynecol. 1975 Mar 1;121(5):704-6. doi: 10.1016/0002-9378(75)90476-7.
A double-blind clinical study was performed to determine whether the release of progesterone from an intrauterine contraceptive device (IUD) had any effect on IUD event rates. A total of 101 women received intrauterine contraceptive devices containing progesterone, resulting in the accumulation of 877 women-months experience; 100 women received IUD's without steroid, resulting in the accumulation of 780 women-months. The only significant difference was a higher incidence of pregnancy in those patients using devices which did not contain progesterone.