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Intrauterine System (IUS)

Some of the latest coils slowly release hormones into the womb over a period of anything up to 5 years. This type of device is called an intrauterine system and is inserted in a similar way to a standard IUD. The IUS has a higher effectiveness rate than the standard IUD because of the hormone it releases. It thins the lining of your womb so that there is less bleeding and the womb is less likely to be fertilized by an egg. It may also prevent ovulation (egg release) in some women.

One hormone used in IUS’s is Levonorgestrel which is a progestogen (a synthetic version of the natural hormone progesterone) and is called commercially Mirena IUS. Progestasert is another effective IUS available but must be replaced yearly. Less than 1 in 100 will fall pregnant on this IUS (about the same effectiveness rate as the Pill).

Progestasert IUS and Mirena IUS release progesterone into the uterusmay cause pelvic inflammatory disease or worsen existing infection
periods become much shorter and lighter. 1.5 times greater risk of getting a pelvic infection than on another method of birth control
effective immediatelysterility due to scarring of the fallopian tubes by pelvic infection
sex is not interruptedmore bleeding or cramping with periods
easily reversed discomfort and bleeding for a few hours or days after the IUD is inserted can occur
Mirena has lower failure rate than the Combined Pill because levonorgestrel adds to the contraceptive effect sometimes an IUS may fall out and this is more likely to happen during a period
useful form of contraception if you suffer from painful periods or heavy or prolonged blood loss, which leads to anemiamedical risks sometimes include infection or puncture of uterus or problems with pregnancy

It is possible that:

  • period pain may be reduced
  • you may get irregular bleeding during the first few months
  • your periods might stop altogether
  • Mirena has a low risk of ectopic pregnancy

Side effects include:

  • backache
  • lower abdominal pain
  • those listed for standard IUD

Possible side effects of the hormone include:

  • acne
  • breast tenderness
  • headaches
  • ovarian cysts (no connection with polycystic ovary syndrome)
  • spots
  • weight gain

As Levonorgesterel, the hormone in Mirena, has been in widespread use for only a short period of time, long term effects of the hormone are as yet unknown.

A good source for more information is the detailed book “Mirena: The Levonorgestrel Intrauterine System: The New Contraceptive Option for Parous Women” by E. D. B. Johansson.


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