Hormone levels independent of BMI with contraceptive implant

1. After at least one year of contraceptive implant use, there was no difference in hormone level across BMI categories.

2. No participant fell below the 90 pg/mL therapeutic threshold for ovulation suppression.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Nearly two-thirds of reproductive-age women in the United States are overweight or obese. The contraceptive implant, commercially known as Nexplanon, is a long acting reversible contraceptive (LARC) method that is inserted under the skin and releases a small amount of progestin hormone (etonogestrel) for up to three years. It is the most effective form of birth control currently available and estrogen-free, making it a desirable option for overweight and obese women who may be at increased risk of blood clots when using more popular estrogen-containing methods like the pill, the patch or the ring. Some experts are concerned that hormonal contraceptive methods may not be as effective in obese women, a thought process supported by preliminary evidence. Biologically, obese women could plausibly have an increased volume of distribution and altered plasma clearance of progestin. In this study, researchers assessed progestin hormone levels in implant users across BMI categories.

After at least 1 year of implant use, there was no significant difference in serum hormone level by BMI and no participants fell below the 90 pg/mL therapeutic threshold suggested for ovulation suppression. Strengths of this study included clinical BMI measurement and serum circulating hormone level after at least one year of use, since the amount of progestin released from the implant decreases over time. Limitations included the small sample size, self-reported BMI data and homogenous population composed of primarily Hispanic women. Future studies should employ a larger, ethnically diverse sample and follow-up throughout the duration of the implant (3 years).

Click to read the study in Contraception

Relevant Reading: Pharmacokinetics of the etonogestrel contraceptive implant in obese women

In-Depth [cross-sectional study]: A convenience sample of normal-weight (BMI <25 kg/m2, n = 10), overweight BMI 25-30 kg/m2, n = 19), and obese (BMI ≥30 kg/m2, n = 23) women using the contraceptive implant for at least one year were recruited from a Family Planning Clinic and private practice in New York. Participants provided demographic and clinical information by questionnaire and a blood sample to measure serum etonogestrel levels.

The median time since implant placement at the time of hormone level assessment was 35 months (range 13-54 months). Etonogestrel levels were comparable across BMI categories (normal: 216 pg/mL, overweight: 288 pg/mL, obese: 225 pg/mL; p = 0.1). No participant fell below the 90 pg/mL threshold suggested for ovulation suppression. There was a non-significant trend observed whereby etonogestrel level decreased as a function of time since implant insertion (p = 0.08)

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