Timing of onset of contraceptive effectiveness in Norplant® implant users II -: Effect on the ovarian function in the first cycle of use

The objective of this study was to time the onset of contraceptive effectiveness in Norplant(R) implant users, when the capsules were inserted beyond the first 7 days of the cycle, based on the immediate effect on the ovarian activity. A total of 42 healthy women requesting Norplant implant contraception were enrolled at clinics in Santo Domingo, Dominican Republic, and in Baltimore, Maryland. Implants were inserted on days 8-13 of the menstrual cycle. Blood samples for estradiol (E-2), progesterone (P), luteinizing hormone (LH) (in a subset of 12 women), and levono-gestrel (LNG) assay, were taken at 0 h and at 6, 12, 24, 72, and 168 h postinsertion. Ovulation, as defined by P > 2.5 ng/mL, occurred in 40% of subjects. A short lasting, frequently blunted, LH peak occurred within 12 h postinsertion, in all these subjects. The remaining subjects had anovulatory cycles with two distinct E-2 profiles: continuously increasing E-2 levels to a high mean of 414.3 pg/mL (28%), or no sustained increase in E-2 (32%). Most cycles (86%) in which Norplant was inserted with high E-2 levels (> 175 pg/mL) were ovulatory, whereas none were ovulatory with low E-2 (< 100 pg/mL) at insertion. Based on the endocrine effects of Norplant implant insertion in the midadvanced follicular phase, in which ovulation will either occur within 48 h of insertion or will be impaired, additional contraceptive protection is necessary only for 3 days. CONTRACEPTION 1999;59:245-251 (C) 1999 Elsevier Science Inc. All rights reserved.