The lowdown on the Mirena coil

Whilst it may not be the perfect choice for every woman, it can be a game changer for those that it does work for. Not only does it provide reliable contraception, but it can also be an effective treatment for women:

• With heavy, painful periods,

• With endometriosis and adenomyosis

• Women in the perimenopause when periods can often become erratic and prolonged

• Receiving hormone replacement therapy (HRT) in the menopausal transition alongside oestrogen

Exactly what is it and how does it work?

It’s a small, plastic, T-shaped device that sits in the uterus (womb). It contains a type of synthetic progesterone (not identical to the progesterone our body produces, but similar) called Levonorgestrel.

It’s the action of this hormone that thins the endometrium (the lining of the womb), making periods lighter over time for the majority and getting rid of them completely in up to 40%. The contraceptive effect comes mainly from its ability to thicken the cervical mucus, making the womb impenetrable to sperm.

Most women will continue to ovulate and produce their own oestrogen, meaning that even though you may not menstruate (because the endometrium is so thin), you may still feel the natural rhythms of your cycle in other ways, like bloating premenstrually.

How well does it work?

It’s very effective in terms of contraception; less than 1 in 200 women using it will become pregnant (much less than the failure rate of female sterilization even, which is at least 1%). And it can last up to 8 years when used for contraception (but less if it is used for other reasons).

There is no long-term effect on your fertility once it is taken out; you can get pregnant soon afterwards.

Any other plus points?

Well, compared to taking a synthetic progesterone in the form of a pill, injection or implant, the circulating level of progesterone with the Mirena is much less, as the progesterone in the coil works locally within the womb rather than by being absorbed into the bloodstream. This means that women who are sensitive to side effects of other contraceptive methods containing synthetic progesterone, may fare better with this.

All sounds good! So, what are the downsides?

The research shows that 80% of women that use the Mirena are happy with it (compared to 55% of women using the pill). That’s a huge number of satisfied women but it doesn’t work for everyone. In my experience, these are the two most common reasons:

1. Troublesome bleeding

Some degree of prolonged, irregular, or frequent bleeding or spotting is likely within the first 6 months and can be unwelcome and disruptive, especially if it wasn’t expected. For those that can persevere, it will settle by 3-6 months in most cases (up to 50% have troublesome bleeding in the first 3 months, which

drops to 10% by month 6 and 5% by month 9).

I find that if women are mentally prepared for this possibility, it’s easier for them to ‘look through the gap’ and stick with it, as they know it’s likely to settle eventually. However, women that aren’t informed in wdvance, especially if they’ve been enticed by the idea of no periods, will often feel hugely disappointed. Lighter periods and no periods do come, but it does take some time to get there.

2. Hormonal side effects

Some women are exquisitely sensitive to synthetic progesterone. The daily dose of progesterone from a Mirena coil is a fraction of that seen with other progesterone containing methods as I mentioned earlier, but nonetheless, some women will still experience unacceptable side effects (acne, water retention, mood changes and low libido).

Some will feel able to put up with these because of the benefits they otherwise get from the coil. And they should be aware that these symptoms will often become less apparent with time because the level of progesterone in the mirena drops the longer you have it. For example, at 5 years, the daily progesterone dose has halved (this is why some women will get their periods back towards the end of a mirena’s life).

However, for some women these symptoms, or even the potential for these symptoms, will outweigh any benefits of the Mirena, meaning that it just isn’t the right choice for them.

But how will I know if I’m going to be one of the 20% that doesn’t get on with it?

There are levonorgestrel containing oral contraceptive pills out there (Microgynon and Rigevedon for example), so if you’ve ever taken one of these and you’ve felt well, it’s likely you’ll be fine. And whilst other progesterone containing contraceptives may not have levonorgestrel in them, getting on well with other types of synthetic progesterone may also be an indicator (although not a guarantee) that you will tolerate it well, especially given the lower daily dose of synthetic progesterone with the Mirena.

The other common reason for a woman to ask for it to be taken out early, is the troublesome bleeding. It’s less common for this to last beyond 6 months (10%) but not unheard of and some women, just don’t want to put up with that. I find though that if you give women the worst-case scenario of what to expect, they feel more prepared to ride it out than if it comes as a shock.

Lastly, and it may sound obvious given what I’ve said about it stopping 40% of women’s periods, if a woman for personal, cultural or religious reasons, would like to have a regular period every month, then this is not the best choice for her.