Ultrasound localisation of non-palpable Implanon

Background: Localisation of the non-palpable Implanon is useful to confirm its presence or to assist the surgeon with its removal. Previous studies have suggested that almost all non-palpable Implanon implants can be located with ultrasound in phantoms. Aim: To determine whether diagnostic ultrasound is a reliable method for localising non-palpable Implanon implant in-vivo. Methods: Ultrasound was carried out to localise the non-palpable Implanon implant. To ascertain the accuracy of the ultrasound findings, all patients were followed-up until the implant was removed or until it was proven absent by serial progesterone levels confirming ovulation or by negative etonogestrel levels. Results: In 22 out of 23 patients the Implanon was correctly identified as present. The specificity is 95.7% (95%CI 79.0-99.2%), the positive predictive value is also 95.7%. In six out of seven patients the Implanon was correctly identified as absent. The sensitivity is 85.7% (95%CI 48.7-97.4%), the negative predictive value is also 85.7%. Four patients were excluded due to incomplete follow-up. Conclusion: Ultrasound is a reliable first line method for localising non-palpable Implanon. When the Implanon is localised on ultrasound, it is very likely present. When the Implanon is not seen on ultrasound, etonogestrel determination should be carried out to confirm its absence.