Complications of the insertion procedure can include: perforation - This is a rare but potentially serious complication where the Mirena® device passes through the wall of the uterus into the pelvic area, usually at the time of insertion but can very occasionally occur later. This can occur in about one per 1000 insertions. This requires surgery under a general anaesthetic to remove the Mirena®. expulsion - Sometimes the Mirena® device may be partially or completely pushed out by the uterus. It occurs in about 5 per 100 insertions. It is important to check for the threads after each period in the first few months after insertion. infection - Pelvic inflammatory disease (PID) The risk of PID is also related to exposure to sexually transmitted bacteria (chlamydia and gonorrhoea). It is most often seen in the first 3 weeks after insertion due to an existing infection. It is important that you consider carefully your potential risk of acquiring an STI throughout the whole period of time you have the Mirena® device in place. PID may in some cases lead to infertility. pregnancy - The chance of pregnancy is 1 in 1,000. In the rare event of a pregnancy with a Mirena® in the uterus there is a small risk of a miscarriage or ectopic pregnancy (a pregnancy outside the uterus – most often in the Fallopian /uterine tube). This is an uncommon complication and less common than amongst women who are not using any contraception. An ectopic pregnancy may present with abdominal pain or bleeding.