Estradiol plasma levels during long-term treatment with norplantR subdekmal implants

Estradiol (E₂) plasma levels were assessed in forty-seven women treated for one through seven years with the same set of Norplant^R implants. Each woman was subjected to one (n = 34), two (n = 11) or three (n = 2) sampling runs. At each sampling run, blood samples were drawn every third or fourth day during 5 or 6 consecutive weeks. Sampling runs were classified as ovulatory (n = 11), anovulatory (n = 49) or uncertain (n = 1) according to progesterone levels. Controls were Copper T users (n = 8), all classified as ovulatory. No significant differences were found for the mean E₂ levels between Norplant^R users and Copper T users and between ovulatory and anovulatory cases. The mean of the peak E₂ value found in each sampling run was significantly higher in anovulatory Norplant^R subjects than in the control group. The mean of the minimum E₂ level observed was significantly lower in Norplant^R cases than in Copper T users. A single woman from the Norplant^R group and none from the Copper T group had all E₂ values below 370 pmol/l. The inhibition of the reproductive function induced by Norplant^R implants is associated with a wider range of E₂ circulating levels. None of the values observed at the extremes should cause serious concerns. High peaks are transitory and opposed by the antiestrogenic effect of levonorgestreJ. Persistent low levels which could be associated with a hypoestrogenic state were observed in a single case.