Contraception with long acting subdermal implants: I. An effective and acceptable modality in international clinical trials.

This paper presents results of a double blind, multi-centered and multi-national study of two progestin only subdermal implants used for contraception. A regimen of six capsules of levonorgestrel (Ng) used by 492 women had a net cumulative 12-month pregnancy rate of 0.6 percent and a continuation rate of 74.6 percent. 498 women used six capsules of norgestrienone (R2010) and experienced a net cumulative 12-month pregnancy rate of 3.5 percent and a continuation rate of 79.4 percent. The difference in the pregnancy rate was significant at P less than 0.01, while there was no significant difference in the continuation rates. Menstrual problems were the principal reason for termination of the levonorgestrel regimen, accounting for approximately half of all terminations. There were significantly fewer menstrual problems among users of the norgestrienone (R2010) capsules; the net cumulative 12-month termination rate for this reason was 4.3 percent. Results are compared with continuation and termination rates for acceptors of the Copper T 200 at the same clinics. The low pregnancy rate and reasonably high continuation rate of the norgestrel implants coupled with the fact that the expected effective lifetime of a set of capsules is of the order of 3-5 years appears to warrant further development of this contraceptive regimen.