A collaborative study of the progesterone intrauterine device (Progestasert). The World Health Organization Task Force on Methods for the Regulation of Implantation.

A randomised double blind study of a plain T-shaped IUD and an active T-shaped IUD releasing 65 micrograms/day of progesterone, has been completed in four centres. A study of 1320 progesterone-releasing IUD's in parous women for 9660 women months of use significant to 18 months, gave a pregnancy rate of 1.0 +/- 0.4, expulsion of 4.7 +/- 0.6 and removals for pain and bleeding of 6.0 +/- 0.7. A detailed analysis of the menstrual bleeding patterns in these patients gave details of the number and length of bleeding and spotting episodes, count of bleeding days, and count of spotting episodes and days for four one-hundred-day reference periods. While the plain IUD contributed a significant number of intermenstrual spotting and bleeding days, the progesterone-releasing IUD contributed more spotting days.