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Hormonal IUD

Bandolier has been asked by GPs about the effectiveness and cost effectiveness of the Mirena® IUD device sold in the UK by Pharmacia-Leiras. Here we examine trials of effectiveness, but as explained below, we duck the question of cost.


The Mirena system is a plastic T-shaped frame with a steroid reservoir containing 52 mg levonorgestrel (LNG) designed to release about 20 µg LNG per day. It is a minor variant of a previous device (LNG 20)

How it works

The contraceptive device delivers LNG to the endometrium after insertion. This makes the endometrium unresponsive to oestradiol. The endometrium becomes inactive and atrophic so that menstrual shedding is reduced. The inactive endometrium also produces less prostaglandin, so dysmenorrhoea is also reduced. Changes in the endometrium take place irrespective of ovarian function and are a result of the local action of LNG. Thickening of cervical mucus also occurs, making penetration of sperm less likely.

Randomised trials

There are four randomised trials which compare the LNG 20 µg/day intrauterine system (IUS), the precursor of Mirena, with other IUDs. All trials were open, and used copper IUDs for comparison; two [1,2], each of 5-years duration, used the Nova T and two, one of 7-years duration [3] and the other of 3-years [4], the TCu 380 Ag.

Because trials have reported at various stages, Bandolier has taken the longest time period available, though the device has a three year licence in the UK. The most thorough report [1] is examined in detail, with information from others as appropriate. There is also a useful review of the trials [5].

Contraceptive effectiveness

The gross cumulative pregnancy rates in percentages are shown in the L'Abbé plot, together with the number of women in each trial using the LNG-20.
The grouping of points, each of which represents one trial, below the line of equality shows that pregnancy rates with LNG-20 were consistently lower than control. This was statistically significant in three of the trials. The average pregnancy rate for all four trials was 0.6% at an average of five years. The review of four IUDs concluded that the LNG-20 was associated with the lowest pregnancy rates.

Ectopic pregnancy

Two studies reported ectopic pregnancy rates as events per 100 woman years. A rate of 0.02 per 100/woman years was found in [1], ten times less than the ectopic rate for Nova T. No ectopic pregnancies were reported in [3] with LNG-20, compared with a rate of 0.05/100 woman years for TCu 380 Ag.

Pelvic inflammatory disease

The same two trials reported the incidence of PID. In [1] the cumulative 5-year occurrence was 2.2% for Nova T and 0.8% for LNG-20. In the comparison with TCu 380 Ag [3] the rate per 100 woman years was the same , 0.7, in both groups.


There seems to be no real difference in expulsion rates.


LNG-20 is associated with a higher rate of amenorrhoea than other IUDs (five-year cumulative rate of discontinuations in [1] of 6% for LNG-20 compared with 0% for Nova T), especially in younger women.

Hormonal effects

Because some steroid is absorbed into the circulation, there tends to be a higher rate of discontinuation with LNG 20 because of symptoms associated with contraceptive steroid use (12% compared with 2% in [1]).

Bleeding problems

Discontinuations with bleeding problems were significantly lower with LNG-20 (14% compared with 21% in [1]). The discontinuation rates over 5 years because of heavy or prolonged menstrual blood flow were very significantly lower with LNG-20. Moreover, because the mean number of days with bleeding fell to lower levels with LNG-20, haemoglobin levels rose in women on LNG-20 by 1.6 g/L after 5 years compared with a fall of 2.6 g/L in women using Nova T [1].

Cost effectiveness

Bandolier could find no information on cost effectiveness. Trying to compute it is no easy matter, and beyond Bandolier's resources. It will be a complex issue, with the much higher cost of the device (licensed for three years in the UK) set against lower costs from unwanted and ectopic pregnancy and better overall health gains.


  1. K Andersson, V Odlind, G Rybo. Levonorgestrel-releasing and copper-releasing (Nova T) IUDs during five years of use: a randomised comparative trial. Contraception 1994 49: 56-72.
  2. T Luukkainen, H Allonen, M Laukkamaa et al. Five years' experience with levonorgestrel-releasing IUDs. Contraception 1986 33: 139-48.
  3. I Sivin, J Stern. Health during prolonged use of levonorgestrel 20 µg/d and the copper TCu 380 Ag intrauterine contraceptive devices. Fertility and Sterility 1994 61: 70-7.
  4. Indian Council of Medical research Task Force on IUDs. Randomised clinical trials with intrauterine devices: a 36-month study. Contraception 1989 39: 37-52.
  5. I Chi. The TCu 380A (Ag), MLCu375 and Nova T IUDs and the IUD daily releasing 20 µg levonorgestrel - four pillars of IUD contraception for the nineties and beyond? Contraception 1993 47: 325-47.

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