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Clinical trials with IUDs releasing retroprogesterone.


 T-shaped IUDs containing 6-dehydroretroprogesterone in a silastic membrane were constructed in the effort to investigate the long-term in vivo and in vitro release rates of this steroid from a silastic capsule and document local endometrial effects, vaginal bleeding pattern, contraceptive efficiency and patient acceptance. The release rate of the steroid averaged 90 mg daily. The IUDs were inserted into the uteri of 100 sexually active women of reproductive age. The length of the menstrual cycle, duration and pattern of the menstrual flow, inter-menstrual bleeding and pelvic pain were recorded by each patient throughout the study. Endometrial biopsies were performed at intervals varying between 1 and 12 months in 64 women and the tissue was examined histologically for evidence of progestational suppression. The study was terminated because of a pregnancy rate of 6.7/100 women year. When endometrial biopsies were examined, normal endometrium was recovered in over 1/2 the cases. IUDs releasing progesterone, in doses of 150 mg daily, yielded suppressed endometrium over 95% of the time. It seems that contraceptive effectiveness of intrauterine progestins is related to their ability to induce decidual and suppressive changes in the endometrium, suggesting that endometrial changes may play a significant role in the mechanisms of contraceptive action of intrauterine progestins.
