Comparison of plasma etonogestrel concentrations sampled from the contralateral-to-implant and ipsilateral-to-implant arms of contraceptive implant users

Objective: To compare plasma etonogestrel concentrations sampled from the contralateral- versus ipsilateral-to-implant arm. Study design: Sub-analysis of a cross-sectional study in Botswana in 33 participants who provided contralateral and ipsilateral blood samples. Results: Plasma etonogestrel concentrations in contralateral and ipsilateral specimens were highly correlated (correlation coefficient = 0.99; p < 0.0001). Bland–Altman analysis of agreement showed that etonogestrel levels were on average 5.9 pg/mL higher (2.1%) in ipsilateral compared to contralateral specimens (95% confidence interval: −4.1, 15.9 pg/mL). Conclusions: We found no meaningful differences in plasma etonogestrel concentrations between samples taken from the contralateral- versus ipsilateral-to-implant arm. Implications: Our data suggest that etonogestrel plasma concentrations are unlikely to be meaningfully different between samples drawn from the ipsilateral- versus the contralateral-to-implant arms in etonogestrel contraceptive implant users.