A new technique for introducing IUDs into rat uteri.

Virgin female Wistar rats 90-100 days old were fitted with IUDs of monofilament nylon by means of an inserter made of 4 inch thin-wall 20 gauge hypodermic needle passed through either of the cervical canals and into the uterine horn for a distance of 32-35 mm. Rats were mated after IUDs were in place at least 4 weeks and killed between Days 10-21 of pregnancy to test insertion method. Analysis of rats pregnant in one horn (34) to total rats with IUD insertions (41) reveals that the method was 83% effective in preventing pregnancy (78% retention effectiveness). Subsequent use of this method gave 92% retention effectiveness. Visible accumulation of fluid in 54% was not related to contraceptive action of IUDs. It is believed that this method of applying a nylon double device through the cervical os is superior for studying physiological and biochemical factors involving IUDs in the rat.