The Mirena coil is a type of contraception for women. Some women should not use a Mirena coil after cancer treatment.
What the Mirena coil is
The Mirena coil is an intrauterine system (IUS). And although it is similar to a contraceptive coil (IUD) it works in a different way.
You have the Mirena coil put into your womb like the contraceptive coil. But unlike the contraceptive coil, it releases a small amount of a man made hormone into your womb every day. This is levonorgestrel – a man made version of the hormone progesterone. It helps to prevent pregnancy in 2 ways:
- by thickening the mucus at the neck of the womb making it difficult for sperm to enter the womb
- by stopping the womb lining from thickening making it difficult for fertilised eggs to settle in the womb
Because the lining of the womb doesn’t thicken, you may have much lighter periods. Or your periods may stop completely. In fact, some women have this type of coil put in to help make heavy periods lighter.
Who shouldn’t use the Mirena coil
The manufacturers of the Mirena coil say that women shouldn’t use it if they have had:
- cervical cancer or womb cancer
- liver cancer
- hormone dependent cancers, including breast cancer
- blood cancers, including leukaemia
- gestational trophoblastic tumours, such as molar pregnancy
The Mirena coil may affect how your liver works. If you have had liver cancer or any type of liver disease, you should not use the Mirena coil.
Hormone dependent cancers, including breast cancer
Although the Mirena coil only releases a small amount of levonorgestrel, we are not sure how much of it, if any, goes to other parts of the body. Because of this, the manufacturers don't recommend using the Mirena coil if you have had hormone dependent cancers, including breast cancer.
Currently, there is no strong evidence to show whether or not the Mirena coil could cause cancers that depend on hormones to grow. There has been research looking at whether there is a link between the Mirena coil and the risk of breast cancer. The findings from these studies have been mixed.
A recent Norwegian study didn’t find a link between this type of coil and breast cancer, but some other studies have found a link. However, studies often have limitations. For example, they sometimes cannot account for other factors that we know are linked to a woman's risk of breast cancer such as weight or how much alcohol they drank.
If you are concerned you can talk to your GP or specialist about what contraception is best for you.
Blood cancers, including leukaemia
If you have a blood cancer such as leukaemia and have a Mirena coil, any bleeding caused by the coil would be much heavier. This is because you may not have enough platelets to help your blood clot normally.
The manufacturers of the Mirena coil say it may be used with caution if your leukaemia is in remission.
Gestational trophoblastic tumours, such as molar pregnancy
The manufacturers recommend that you do not use the Mirena coil if you have recently been diagnosed with a gestational trophoblastic tumour (GTT), such as a molar pregnancy or choriocarcinoma. They say you should not use this type of coil while your HCG levels are still raised.
Your specialist will advise you about this.