Abstract
Implanon® is a long-acting reversible contraceptive method, consisting of a single
rod that is applied subdermally. Ovulation inhibition was determined by serum progesterone
(P) levels and ultrasound scanning (USS) of the ovaries. Ovarian function was further
assessed by serum estradiol (E2) levels. The effects of Implanon on serum gonadotropin levels (follicle-stimulating
hormone [FSH] and luteinizing hormone [LH]) and on cervical mucus were also investigated,
by means of Insler scores and sperm penetration tests. The effect on the endometrium
was assessed by endometrial biopsies and USS. The Pearl index was calculated over
13 studies performed according to Good Clinical Practice (GCP), including 1716 women
using Implanon. Return of ovulation after implant removal was determined by P levels
and USS of the ovaries.
The contraceptive efficacy of Implanon was high, with zero pregnancies during 53,530
cycles (4103 woman-years), resulting in a Pearl index of 0.0 (95% confidence interval,
0.00–0.09). This was achieved by inhibition of ovulation, which was reflected by suppressed
P levels, as the primary mode of action. Ovulation was inhibited, but otherwise ovarian
activity was still present (follicle growth, E2 synthesis). The FSH serum concentrations were only slightly lower than preinsertion
levels and LH surges were prevented. The viscosity of the cervical mucus was increased.
The endometrium was thin but not atrophic; it showed primarily inactive or weak proliferation.
Return of ovulation after removal of Implanon was rapid.
Keywords
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Copyright
© 1998 Elsevier Science Inc. Published by Elsevier Inc. All rights reserved.
