potency of the steroids they release the higher the progestational potency of the compound the greater the decrease in menstrual bleeding it has also been shown that there is a dose dependent effect on initial bleeding in a clinical comparison trial with different intrauterine systems incl copper and progestin lng containing systems the study was performed in the mid 39 90s by the instituto mexicano del serguro social 7 the study showed that women treated with 8 u03bcg d lng showed a greater decrease in menstrual bleeding compared to the group treated with 2 u03bcg d 7 pedron 1995 adv contra deliv syst vol 11 245 however although a higher initial progesterone release could effectively address the problem of the initial bleeding and spotting the upper dose is limited by the systemic side effects which are caused by the respective progesterone e g lng therefore levonorgestrel as used in mirena u00ae and investigated in the a m comparison trial although suited in principle in terms of the present invention is less advantageous in comparison to 18 methyl 15 u03b2 16 u03b2 methylene 19 nor 20 spirox 4 en 3 one in the context of this application also referred as new progestin np which shows a low systemic stability higher plasma clearance and higher progestional activity compared to lng in some implementations 18.