Pregnancies associated with etonogestrel implants in the UK: comparison of two 5-year reporting periods

(1) To identify pregnancies associated with the use of the contraceptive implants Implanon and Nexplanon in the UK during two 5-year reporting periods. (2) To classify the possible reasons for device failure in cases reported for each implant. (3) To examine any differences between reasons for pregnancies associated with these products.

Extraction of data from the UK spontaneous reporting system for adverse drug reactions in relation to etonogestrel implants. Reports indicating pregnancy were identified for the periods 2005-2009 (Implanon) and 2012-2016 (Nexplanon). Possible reasons for failure of the method in each reported case were assigned to one of eight predetermined categories.

After exclusions, 229 Implanon and 234 Nexplanon cases contained sufficient information for analysis. True method failures accounted for a majority of the pregnancies in those using contraceptive implants (58%); the next most common cause was missing implants (26% of pregnancies). In all categories of cases, there was no difference in frequency of pregnancy when the two time periods were compared.

There is still potential for greater avoidance of pregnancies associated with etonogestrel implant use.

This study underscores the continuing need for taking a full drug history, timing the insertion on days 1-5 or according to recommended quick starting routines and palpating the arm after implant insertion.