The association between BMI and continuity of etonogestrel (ENG)-releasing implant

The etonogestrel-releasing implant is a long-acting reversible contraception that is recommended by the Food and Drug Administration for 3 years and has been proven to be highly effective and convenient. Adverse effects including irregular bleeding patterns, weight gain, and acne are reported to be the main reasons for treatment discontinuation. The aim of this study is to learn the association between body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) and the incidence of side effects and adherence to treatment.

This is a retrospective cohort study, conducted at a single university-affiliated medical clinic, including all women who underwent etonogestrel-releasing implant (Nexplanon®; New Jersey, USA, Organon USA Inc., Merck and Co) insertion between January 2019 and December 2021. Cases where abnormalities were reported during the insertion procedure or missing data were excluded from the study. Information on patients' demographic, medical history, obstetric and gynecological history, and follow-up was collected from electronic medical files. The primary outcome was defined as the rate of implant removal in the different obesity classes. Data are presented as median and interquartile range. The study was approved by institutional review board.

The study population included 1318 women, of whom 466 (35%) requested early removal of the implant. Women's demographic and clinical characteristics were comparable between women who requested early removal and those with full-length treatment. The median time for early removal was 12 (6-20) months from insertion. Irregular bleeding was the most frequent reason for early removal in both groups and was more than twice as prevalent in the early removal group (239 [51.29%] vs 193 [22%], P = 0.001). The early removal group had fewer obese women (BMI ≥30) compared with women who had full-length treatment (163 [31.8%] vs 350 [68.2%], P = 0.03), with comparable rates of class 3 obesity women (BMI ≥40) (P = 0.68). Multi-regression logistic analysis including age, BMI, parity and side effects found that the presence of side effects is the only independent predictor significantly associated with early implant removal (B = 1.74, P = 0.04).

Continuation of etonogestrel-releasing implant contraception treatment was associated with the presence of side effects that were more often reported in non-obese women. BMI was not found to be a significant factor influencing adherence to treatment.