Section 1: Hormonal emergency contraception
There are two methods of emergency contraception (EC) in current use: the 1.5mg levonorgestrel pill or an IUD.
Levonorgestrel 1.5mg should be given within 72 hours of the first unprotected sex in that cycle. An IUD can be fitted up to five days after the earliest predicted date of ovulation, even if there have been multiple exposures.
All women requesting EC should be fully counselled regarding the failure rates of oral and intrauterine EC to allow them to make an informed choice, even if they attend within 72 hours of unprotected intercourse.
Until a few years ago, the predominant hormonal method of EC was the Yuzpe method, or Schering PC4, which consisted of both estrogen and progestogen. However, PC4 has been superseded by the more effective and safer progestogen-only method, levonorgestrel 1.5mg (Levonelle), which was licensed late in 1999 and launched in February 2001.
A WHO study showed that the efficacy of levonorgestrel 1.5mg is the same regardless of whether the dose is split into two pills taken 12 hours apart, or both together.1,2 Clearly, taking two pills at once is much simpler and therefore likely to improve compliance.
Mode of action
If given before ovulation, levonorgestrel 1.5mg tends to delay ovulation, rather than prevent it, so use of a barrier method until the patient's next period is mandatory.
It is also likely that it causes interference with sperm motility, preventing fertilisation.
There is some debate as to whether, if given after ovulation, hormonal EC prevents implantation. Recent studies have suggested that the rate of ovulation suppression is approximately equal to the effectiveness of hormonal EC pills,3 suggesting that this might be the only mechanism by which they prevent pregnancy.
Pregnancy is not said to have occurred until after implantation, so even if levonorgestrel can prevent implantation this action is not abortifacient. However, some religious groups take a different view and this may need to be considered when counselling.
Efficacy of levonorgestrel
The efficacy of postcoital contraception can be presented in different ways. However, currently the most commonly used is the calculation of the number of pregnancies prevented. This method uses assumptions on the probability of conception on any given day of the cycle, and compares that with the number actually observed.
It is therefore not possible to give precise figures, but studies of the levonorgestrel regimen suggest that, taken within 72 hours of the first unprotected sexual intercourse in that cycle, levonorgestrel 1.5mg prevents between 59 and 94 per cent of pregnancies. Two randomised trials comparing the combined regimen with levonorgestrel 1.5mg found the latter to be twice as effective.4
Some studies have found that hormonal EC is more effective if the pills are taken within 48 hours, as opposed to 72.5
It has also been shown that use of levonorgestrel 1.5mg may be extended up to 120 hours after unprotected intercourse, with some reduction in efficacy.1 It should be remembered that, although supported by evidence, such use is off licence.
Women should use a barrier method of contraception until their next period, as pregnancy could still occur after levonorgestrel 1.5mg has been taken.
Section 2: Disadvantages of hormonal EC
The most common side-effect of hormonal EC is nausea, but this is much less frequent with levonorgestrel 1.5mg (around 20 per cent) compared with PC4 (around 50 per cent).
Vomiting is also much less common with levonorgestrel (around 2 per cent compared to 18 per cent with PC4).
Antiemetics are not routinely recommended with levonorgestrel 1.5mg, however, if a woman vomits within two hours of taking it, she should take a further dose as soon as possible.
Temporary disruption of the menstrual cycle is commonly experienced. If taken before ovulation, the high dose of progestogen may induce withdrawal bleeding a few days after the pills are taken.
If levonorgestrel 1.5mg is taken after ovulation, it may increase the length of the luteal phase, delaying menstruation by a few days.
If menstruation is delayed by a week or more, pregnancy should be excluded.
In case of failure
Women should be counselled that, although no guarantee can be given of a normal pregnancy, no excess risk of abnormality has been observed in babies born following use of hormonal EC, nor indeed in those born following failure of regular use of the combined or progestogen-only pills.
In theory, there is a slightly greater risk of the pregnancy being ectopic.
Women should therefore be told to come back if their next period is not normal.
Because the method is now progestogen only, in practice there are virtually no contraindications. It can be given to women who suffer migraine with focal aura, to breastfeeding women, even to those with a history of thrombosis, since progestogen-only methods do not increase the risk of VTE.
Some women request levonorgestrel 1.5mg more than once in a cycle. Each use of levonorgestrel should be viewed as resulting in protected sex, therefore there is no reason why it cannot be given several times in the same cycle.
With repeated use, there may be disruption of the menstrual cycle that month, but this is surely preferable to unplanned pregnancy.
As mentioned previously, the method has essentially no health risks, so repeated use does not pose any greater risk. However, repeated requests should alert the provider to the need for a full discussion of the reasons for this, and to review the woman's contraceptive method.
Enzyme-inducing drugs may reduce the efficacy of levonorgestrel. The current consensus (although there is no actual evidence) is that the dose should be doubled, ie two tablets should be taken. Because of its higher efficacy, an IUD should always be offered under these circumstances.
There is a move towards giving women the emergency pill in advance, especially since it may be more effective if taken within 48 hours. This should be particularly considered for women who use a barrier method as their regular contraceptive, as 'accidents' are especially common in this group. Studies suggest that such provision does not lead to misuse.6
Section 3: Copper intrauterine devices
Although the majority of women prefer to use an oral method of EC, there are circumstances in which the use of an IUD is particularly indicated (see box).
Indications for postcoital IUD insertion
The failure rate of the IUD used postcoitally has been estimated to be no higher than 1 per cent.
It is therefore certainly more effective than hormonal postcoital contraception and should always be offered, especially when maximal efficacy is required.
The IUD is particularly useful in cases of multiple exposure over a longer time period than covered by levonorgestrel 1.5mg. An IUD can be fitted up to five days after the earliest predicted date of ovulation.
So, for example, for a woman with a regular 28-day cycle, it could be fitted up to day 19.
The main mode of action of the IUD is considered to be the prevention of fertilisation, but, if fitted after fertilisation, it can prevent implantation.
If IUD fitting is not performed at first presentation, it is a very good idea to give levonorgestrel 1.5mg in the interim (the belt and braces approach).
Section 4: Disadvantages of the IUD
The side-effects of IUDs for EC are the same as for any use of the IUD. The woman is likely to experience some cramping pain and bleeding following the fitting.
Infection is also a possibility. Her first period following insertion of the IUD is likely to be more painful than usual.
Contraindications to emergency use of an IUD are similar to those for long-term use. Women at high risk of STIs or ectopic pregnancy may be better advised to have the IUD removed after the next period and to use a different form of long-term contraception.
It is advisable to test for chlamydia prior to fitting, even if there is not time to wait for the result (to allow for full treatment and partner notification later in positive cases): antibiotic cover with doxycycline or azithromycin should be considered in such cases.
It is important to note that the intrauterine system (IUS) is not licensed for postcoital contraception and there have been no trials of its use in this way.
Because of its mode of action, it is considered to be unsuitable for emergency use.7
Emergency contraception in the future
A pilot study of 41 women has suggested that adding a cox-2 inhibitor to levonorgestrel 1.5mg may increase its efficacy. This may be useful if confirmed in trials.5
Mifepristone has shown great promise as EC. Two studies have found failure rates of 0 per cent using a 600mg single dose of mifepristone within 72 hours of unprotected sex.8
More recently, two WHO trials have shown using only 10mg of mifepristone to be effective, even up to five days after unprotected sex.1,9
The incidence of nausea and vomiting is similar to that with levonorgestrel. Menstrual delay of up to seven days is common, which may cause unnecessary anxiety.
A second-generation antiprogestin, CDB-2914, has also recently been shown to be at least as effective as levonorgestrel 1.5mg, and its efficacy does not appear to diminish when used more than 48 hours after UPSI.5
1. Von Hertzen H, Piaggio G, Ding J et al for the WHO Research group on post-ovulatory methods of fertility regulation. Low dose mifepristone and two regimens of levonorgestrel for emergency contraception: a WHO multicentre randomized trial. Lancet 2002; 360: 1,803-10.
2. Webb A M. Emergency contraception. BMJ 2003; 326; 775-6.
3. Croxatto H B, Brache V, Pavez M et al. Pituitary-ovarian function following the standard levonorgestrel emergency contraceptive dose or a single 0.75-mg dose given on the days preceding ovulation. Contraception 2004; 70: 442-50.
4. WHO Task Force on Postovulatory Methods of Fertility Regulation. Randomised controlled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency contraception. Lancet 1998; 352: 428-33.
5. Trussell J, Raymond E G. Emergency contraception: A last chance to prevent unintended pregnancy. Available at: http://ec.princeton.edu/questions/ec-review.pdf, accessed June 2009.
6. FFPRHC Guidance: Emergency contraception. J Fam Plann Reprod Health Care 2006; 32: 121-8.
7. Melvin L. Use of IUS as emergency contraception J Fam Plann Reprod Health Care 2009; 35 (3): 205.
8. Cheng L, Gulmezoglu A M, Piaggio G, Ezcurra E, Van Look PF. Interventions for emergency contraception. Cochrane Database Syst Rev 2008 Apr 16; (2): CD001324.
9. WHO Task Force on Postovulatory Methods of Fertility Regulation. Comparison of three single doses of mifepristone as emergency contraception: a randomised trial. Lancet 1999; 353: 697-702.