Levonorgestrel plasma concentrations and hormone profiles after insertion and after one year of treatment with a levonorgestrel-IUD.
Level 4 - case-series / case-control
Prospective single-arm longitudinal case series without a control group
PubMed 6771090 · doi:10.1016/0010-7824(80)90003-7
What was done
Seven volunteers had a levonorgestrel-releasing intrauterine device (designed to release 25 mcg/day) inserted postmenstrually. Blood samples were collected twice weekly during a mean of 93 days post-insertion and during a mean of 41 days across the 12th to 15th months to measure plasma concentrations of levonorgestrel, progesterone, estradiol, FSH, and LH. Bleeding patterns and contraceptive outcomes were monitored over one year.
What was found
Mean (± SD) levonorgestrel plasma concentrations were 260 ± 68 pg/ml during the first 3 months and 129 ± 28 pg/ml after 1 year. Only 2 of the 7 subjects ovulated during the initial blood sampling period, whereas 5 of 7 ovulated after 1 year. Intermenstrual spotting was frequent during the first 60 days, and 3 subjects developed amenorrhea by the end of the first year. All 7 participants completed the year with no pregnancies.
Why it matters
This early study demonstrates that levonorgestrel-releasing IUDs maintain contraceptive efficacy and local endometrial effects over one year despite declining plasma drug levels and the resumption of ovulatory ovarian cycles in most users.
Limits
The sample size is very small (n = 7), limiting statistical power and generalizability. There is no control group, and exact numerical concentrations for progesterone, estradiol, FSH, and LH were not reported in the abstract.
Cited by
- supports A levonorgestrel-releasing (progesterone) intrauterine device typically suppresses ovulation during the first two years of use, after which progesterone levels decline and ovulation typically resumes.