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 77months before this study. Main Outcome Measures Follicle-stimulating hormone, luteinizing hormone, estradiol (E 2 ), 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 E 2 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.