2O'Brien PA, Kulier R, Helmerhorst FM, et al. Copper-containing, framed intrauterine devices for contraception: a systematic review of randomized controlled trials [ J ]. Contraception,2008, 77(5) :318-327.
3Haugan T, Skjeldestad FE, Halvorsen LE, et al. A randomized trial on theclinical performance of Nova 3380 and Gyne I380 slimline copper IUDs [ J ]. Contraception, 2007,75 (3) : 171- 176.
