Ovarian function during use of Nestorone (R) subdermal implants

Nestorone(R) progestin (NES) is a potent 19-nor-progesterone derivative whi ch is biologically inactive when administered orally; however it is an exce llent option for implant contraception. The objective of this study was to evaluate ovarian function during use of either one 4-cm or two 3-cm NES imp lants for 24 months. A total of 60 volunteers were enrolled in each dose gr oup. Vaginal ultrasound (VUS) and blood sampling for determinations of estr adiol (E-2), progesterone (P) and NES serum levels were carried out twice a week for 6 consecutive weeks, beginning in months 1, 6, 12, 18, and 24 of implant use. Serum levels of NES declined with time, with a more pronounced decrease during the first 18 months of implant use; thereafter, NES levels remained stable until the end of the study at 24 months. Luteal activity w as very infrequent during the first year of use (<3%) but increased during the second year, occurring in 27% anti 35% of the sampling periods in the 1 -implant group, and 2% and 16% of the sampling periods in the 2-implant gro up, at months 18 find 24 of use, respectively. No luteal activity was obser ved with NES levels above 80 pmol/L. Serum P levels in periods of luteal ac tivity were significantly lower than those of controls. Persistant anovulat ory Follicles were the most common VUS finding and this was associated with E-2 levels that remained within the normal range (101-1500 pmol/L) in the majority of the sampling periods studied. Considering that a single implant offers advantage for insertion and removal, a new single NES implant is be ing developed with a slightly higher release rate, to reduce effectively th e incidence of ovulation and provide a greater margin of safety beyond 2 ye ars. CONTRACEPTION 2000;61:199-204 (C) 2000 Elsevier Science Inc. All right s reserved.