The present invention describes intrauterine use of 18-methyl-15ß,16ß-methylene-19-nor-20-spirox-4-en-3-ones of the general formula (1) in contraception and gynaecological treatment, and an intrauterine system comprising compounds of formula 1.本發明闡述一種通式(1)之18-甲基-15ß,16ß-亞甲基-19-降-20-螺氧-4-烯-3-酮於避孕及婦產科治療上的用途,及包含式1化合物之子宮內系統。