Insertion forces with intrauterine devices: implications for uterine perforation.

The force required to insert a Copper 7, Multiload Copper or Nova T IUD was measured in 197 successful and 25 unsuccessful insertion attempts. These forces were compared with the forces required to perforate freshly obtained uterine specimens with a metal uterine sound and Dalkon shield device, as well as with the clinically tested devices. The mean insertion forces for the Copper 7, Nova T and Multiload Copper devices were 1.502 N, 2.134 N and 4.041 N respectively, while the mean insertion pressures (N/mm2) were 0.203, 0.209 and 0.122 respectively. The mean in vitro fundal perforation forces with metal sounds was 20.7 N and with the Dalkon shield 31.6 N. The Copper 7, Multiload Copper and Nova T IUDs achieved mean in vitro forces of 5.75 N, 9.2 and 8.1 N respectively, without causing perforation. Primary uterine perforation at the time of insertion of these devices appears unlikely.