Neuroendocrine mechanism of anovulation in users of contraceptive subdermal implant of nomegestrol acetate (Uniplant)

Objective: To evaluate a nomegestrol acetate subdermal contraceptive implant's (Uniplant; Thermex, Monaco) effect on the hypothalamus-pituitary-ovarian axis. Design: A prospective clinical trial. Setting: San Borja-Arriaran Clinical Hospital, University of Chile, School of Medicine. Patient(s): Normally cycling healthy women. Intervention(s): Insertion of Uniplant. Main Outcome Measure(s): Luteinizing hormone pulse and endocrine profiles were assessed before, 48 hours after insertion, and after prolonged use of the implant. Result(s): Anovulation was noted in 100% of users in the first month. Seventy percent of subjects demonstrated follicular development with the absence of ovulation and an endocrine profile similar to the follicular phase: (LH pulse/8 hours 6.85 +/- 0.67, LK amplitude 3.54 +/- 0.65 mIU/mL (conversion factor to SI unit, 1.00), and E(2) 193 +/- 29.4 pg/mL (conversion factor to SI unit, 3.67), whereas 30% demonstrated no follicular activity with an endocrine profile similar to the luteal phase: (LH pulse/8 hours;; 3.66 +/- 0.66, LH amplitude 5.76 +/- 1.73 mIU/mL, and E(2) 67.5 +/- 4 pg/mL. Clinical characteristics, serum gonadotropin concentration, and LH pulse characteristics failed to predict which subjects would initiate or remain devoid of follicular activity. Conclusion(s): Uniplant results in anovulation via two mechanisms: hypothalamic suppression in subjects who lack follicular development, and likely suppression of the pituitary LH surge in subjects who initiate follicular activity.