Ovulatory dysfunction during continuous administration of low-dose levonorgestrel by subdermal implants.
OBJECTIVE: To study the endocrinologic profile of regularly menstruating users of levonorgestrel subdermal implants. DESIGN: Observational, prospective, case-controlled comparative study. SETTING: The Family Planning Clinic of PROFAMILIA, in Santo Domingo, Dominican Republic. PATIENTS, PARTICIPANTS: Thirty one regularly cycling Norplant users and 12 nonhormonal contraceptors who volunteered to participate. INTERVENTIONS: Norplant contraceptive implants were inserted in 31 subjects between 13 and 77 months before this study. MAIN OUTCOME MEASURES: Follicle-stimulating hormone, luteinizing hormone, estradiol (E2), and progesterone (P) were serially assayed for one menstrual cycle. RESULTS: Almost half of the cycles among Norplant users were anovulatory; all the rest (55%) had some form of dysfunction: diminished gonadotropin surge, luteal phase insufficiency (low P levels and shortened luteal phase), and E2 profiles different from normal controls. CONCLUSIONS: Anovulation is clearly one of the main mechanisms of action of Norplant, but even in presumptive ovulatory cycles, the dysfunctions described possibly contribute to the high contraceptive effectiveness of Norplant.