OVARIAN-FUNCTION DURING THE USE OF A SINGLE CONTRACEPTIVE IMPLANT - IMPLANON COMPARED WITH NORPLANT

Objective: To study the mechanism of action of Implanon, a single-rod contraceptive implant containing etonogestrel, in healthy women during 3 years. Design: Prospective, randomized comparison with Norplant. Th e study was conducted for 2 years in Sweden but was extended to 3 year s in Finland. Setting: Two outpatient clinics. Patient(s): Thirty-two healthy women who were between 18 and 40 years of age with normal ovul atory cycles. Seven women receiving Implanon and three receiving Norpl ant participated in the third year. Intervention(s): On or between day s 1 and 5 of a spontaneous menstrual cycle, the subjects received eith er the etonogestrel-containing implant (Implanon) or the levonorgestre l-containing implant (Norplant). Main Outcome Measure(s): Ultrasonogra phy was performed and/or progesterone concentrations were determined t o confirm ovulation in a control cycle. Follicular development, endome trial thickness, and serum concentrations of 17 beta-estradiol and pro gesterone were assessed twice per week during 4-week periods at regula r intervals and after implant removal for 6 weeks to monitor return of ovulation. Times required to remove the respective implants were eval uated, as were possible complications. Result(s): Seven women who rece ived Implanon and three who received Norplant completed 3 years of stu dy. There were revised and accepted no pregnancies. Ovulation was obse rved for the first time with Norplant after 18 months. The first ovula tion with Implanon was observed after 30 months. Mean endometrial thic kness was <4 mm during treatment with Implanon from month 12 onward. T he mean (+/-SD) time to remove Implanon was 5.9 +/- 3.4 minutes. The m ean (+/-SD) time to remove Norplant was 17.9 +/- 9.9 minutes. Ovulatio n resumed promptly after the use of either implant. Conclusion(s): Res ults from this study provide convincing evidence of 3-year contracepti ve efficacy with Implanon,mainly by ovulation inhibition. (C) 1998 by American Society for Reproductive Medicine.).