Intrauterine System (IUS) - the hormone coil
The IUS delivers a small amount of the hormone progestogen into the womb every day for up to
five years. It is a small, plastic T shaped device that your doctor inserts through the vagina and
cervix so that it sits in the womb.
The IUS is an excellent contraceptive (more than 99% effective), but it does not protect against
sexually transmitted infections. It works by thickening the cervical mucus so sperm cannot pass
through the cervix easily. It also keeps the lining of the womb thin, making implantation difficult
and, in some women, may also prevent ovulation.
The IUS is a very effective way of managing heavy, painful periods. It prevents the lining of the
womb from thickening and so women only tend to have very light periods or have no bleeding at
Fitting an IUS can usually be done in the clinic setting. Some women find the procedure
uncomfortable and there is always an option of using local anaesthetic if necessary. First, your
doctor will examine you to assess your womb. A speculum instrument is placed into the vagina
(the same instrument used for taking a cervical smear test). The IUS is passed through the cervix
and sits at the top of the womb. There are two fine threads that are cut just below the cervix. The
threads are important for removing the IUS and you may well be able to feel them yourself. They
should not have any impact on intercourse.
Some women get period-like pains for a few days following insertion of an IUS and should take
some simple painkillers such as paracetamol and ibuprofen. Your doctor will check the position of
the coil 4-6 weeks after the fitting.
Having an IUS fitted is very safe but, as with all procedures, there a few risks. The most common
risks are bleeding and infection. See your doctor if you develop an offensive vaginal discharge as
this may indicate an infection and you may need antibiotics. It is normal to have bleeding after an
IUS and the bleeding may last several months. It is usually light bleeding and spotting. Rarely, an
IUS can be rejected (fall out) or can migrate (make a hole in the womb and travel into the
abdomen). For these reasons it is important that your doctor checks the position of the IUS after it
You are very unlikely to get pregnant with an IUS in situ but you should use additional
contraception for the first seven days after fitting. If you do get pregnant, you have a increased
chance of an ectopic pregnancy and so consult your doctor in this scenario.