Hormone Testing with Mirena IUD
Yes, hormone testing can be performed in patients with a Mirena IUD, but interpretation requires understanding that the levonorgestrel-releasing IUD primarily exerts local effects on the endometrium while having minimal systemic hormonal impact, and most women maintain normal ovarian function.
Technical Feasibility
- Hormone testing is technically feasible and not contraindicated in women with Mirena IUDs 1, 2, 3
- The levonorgestrel-releasing IUD releases low doses of hormone locally, with plasma concentrations ranging from approximately 260 pg/ml in the first three months to 129 pg/ml after one year of use 1
- After 6 years of use, serum levonorgestrel levels remain detectable at mean levels of 314-471 pmol/L, but these are relatively low systemic concentrations 2
Ovarian Function Preservation
- The majority of women with Mirena IUDs maintain normal ovulatory cycles, making hormone testing interpretable for assessing ovarian function 2, 4
- After long-term use (6 years), approximately 78.5% of women demonstrate ovulatory cycles with normal patterns of LH, progesterone, and estradiol 2
- The IUD does not significantly influence follicular maturation, timing of ovulation, or corpus luteum function 4
- Complete suppression of ovulation is rare, occurring in only 14.3% of cases after extended use 2
Clinical Interpretation Considerations
- Hormone testing for fertility assessment, menstrual irregularities, or suspected endocrine disorders can proceed normally in most Mirena users, as the contraceptive effect is primarily due to local endometrial changes rather than systemic hormonal suppression 2
- FSH, LH, estradiol, and progesterone levels typically reflect actual ovarian function rather than being significantly altered by the IUD 1, 2, 4
- The IUD exerts primarily local effects on the endometrium, causing menstrual changes that may not correlate with hormone levels (e.g., amenorrhea can occur despite normal ovulatory cycles) 2, 4
Important Caveats
- While ovarian function is generally preserved, individual variation exists—some women may have anovulatory cycles or luteal phase insufficiency 2
- The presence of amenorrhea in a Mirena user does not necessarily indicate anovulation or hormonal dysfunction, as local endometrial suppression can cause amenorrhea despite normal ovarian hormone production 2
- If testing for pregnancy-related hormones (hCG), be aware that pregnancy with Mirena in place is rare but possible and associated with potential fetal effects if the device remains in situ 5