Health authorities say they do not know how many women in New Zealand are using a contraceptive implant reported to have failed in some cases in Britain.
Some 584 women out of 1 million users of Implanon in Britain are reported to have had pregnancies. The birth control device is implanted underneath the skin.
Medsafe, the authority responsible for the regulation of therapeutic products in New Zealand, says the implant is not subsidised by the Government's drug-buying agency Pharmac and the Health Ministry does not hold data on how widely the implant is used.
Medsafe group manager Stewart Jessamine says the British problems are due to the implant not being inserted correctly.
New Zealand's Family Planning national medical adviser is concerned that the implant failed in some cases in Britain because of the way it was inserted.
Dr Christine Roke says few women in New Zealand use Implanon because there is a much cheaper alternative that is subsidised and lasts longer.
Janelle lasts for five years and costs $3, while Implanon lasts for three years and costs $265.
Dr Roke says if people can feel the single rod implant under their skin, they can be convinced that it will be 99% effective in preventing pregnancy.
There are no plans to withdraw Implanon from use in New Zealand.