Consultant Sexual and Reproductive Health expert Dr Anne Webb answers your questions

Q What is emergency contraception?

A Emergency contraception (EC) is any method which can be used after sexual intercourse which reduces the chances of a pregnancy implanting in the womb. Many methods have been used over time but there are currently three available in the UK. In order of effectiveness they are:

  • Copper intrauterine devices (IUD)
  • Ulipristal acetate 30mg (UPA)
  • Levonorgesterel 1.5mg (LNG)

This article will look at what the clinician should consider during most EC consultations, and explains the theory behind the answers. National clinical guidance is available to all on the Faculty of Sexual and Reproductive Health website:

Q Is EC ever not necessary following a request?

A Emergency contraception should be considered whenever there is a risk of pregnancy and the woman does not wish to be pregnant. A woman needs to be considered at risk of pregnancy after any sexual contact, even without full vaginal penetration, whenever she used no contraception or did not use it effectively or consistently.1 The risk of pregnancy is very low in the first three days of the cycle, but at all other times, there may be some risk.2

Q Can a woman’s risk of pregnancy be quantified to help her choice of method?

A For most of the cycle a woman cannot get pregnant. She is only at risk during a few days, probably no more than a week, leading up to and including the time of ovulation. Within a few hours after this the ovum deteriorates and is no longer fertilisable. Therefore, from the day after ovulation until the next cycle she is not at risk. The highest risk days are the two prior to and including ovulation. This coincides with the luteinizing hormone (LH) rise and peak which induces ovulation in a normal cycle. This means that for roughly three quarters of the cycle, there is no risk. However, even in women with regular cycles, it is not possible to pinpoint, with any accuracy, the time of ovulation just by knowing the length of the cycle and the date of commencement of the last menstrual period (LMP).

Studies have shown that only 10% of women ovulate 14 days before the date of their next expected menstruation.3 More than half of women with regular cycles, and who requested EC, had an LH level above 20 IU/l, indicating they were close to ovulation, but were not within the estimated fertile period according to their date of LMP and cycle length.4 Equally, 14 of 32 women who appeared to be in the luteal phase of the cycle from their dates, showed blood results compatible with not yet having ovulated.5

Other factors can affect the risk of pregnancy including any attempts at barrier contraception and coitus interruptus, or whether any hormones have been used in the recent past. So, although overall most women will not get pregnant even without any EC, it is impossible to give an accurate estimate as to where a woman might be in her cycle, and therefore her individual risk of pregnancy. Only she can decide how important it is to avoid a pregnancy and which method she prefers out of all she is eligible for.

 emergency contraception figure 1Q How effective is EC?

A The copper intrauterine device is known to work, near enough, always, with failure rates significantly lower than 1%. This is because it is effective throughout the pregnancy risk time, as it works both before ovulation and up to implantation.

Oral methods reduce the risk but ongoing pregnancies are still seen and women must be warned to have a pregnancy test if they do not get a period when they next expect it.

Despite a lot of work on the subject we do not know, with any degree of certainty, how many pregnancies oral EC prevents.

The estimate of prevented pregnancies is varied but levonorgesterel appears to reduce the risk of pregnancy by at least half and maybe by as much as 80-90%. It is licenced up to 72 hours but may have some effect up to 96 hours after unprotected sexual intercourse (UPSI), probably depending on where the woman was in her cycle at the time of the UPSI.

Ulipristal has been shown to work up to 120 hours after UPSI with no reduction in effectiveness over time. It is at least as effective as levonorgesterel and appears to work longer during the highest risk time of the cycle.2 This supports the greater effectiveness found in the published metanalysis.

The effectiveness of the different EC methods relates to how they work and therefore when they will be effective. (Figure 1)

Q How do EC methods work?

A The copper intrauterine devices works primarily by preventing fertilisation but can also have a preimplantation effect. It therefore works throughout the pregnancy risk time which explains its high effectiveness.

Both oral methods can interfere with ovulation by inhibiting it. There is no evidence to support any post fertilisation effect of either of these methods.

Levonorgesterel has been shown to inhibit ovulation if given up to the beginning of the LH surge which excludes about two days in the cycle with highest risk of pregnancy.

Ulipristal has been shown to inhibit ovulation during the LH surge but not at the peak which excludes about one day in the cycle at highest risk of pregnancy. It has also been shown to delay ovulation so any subsequent UPSI must be considered to covey a risk of pregnancy.6

Q What if there is a risk of pre-existing pregnancy?

A If a woman is already pregnant there is no point in using EC. Otherwise the Faculty of Sexual and Reproductive Healthcare (FSRH) suggest that health professionals can be reasonably certain that a woman is not currently pregnant if any of the following criteria are met and she has no symptoms of pregnancy:

  • She has not had intercourse since her last menses
  • She has been correctly and consistently using a reliable method of contraception
  • She is within the first seven days of the onset of a normal menstrual period
  • She is within the first seven days of an abortion or miscarriage
  • She is within four weeks of childbirth and is not breastfeeding
  • She is fully or nearly fully breastfeeding and amenorrhoeic and is less than six months from childbirth.7

Q When should a pregnancy test be carried out prior to EC?

A If pregnancy cannot be excluded by the above criteria, a pregnancy test can exclude any pregnancy conceived at least three weeks before. If the risk was between two and three weeks previous, a pregnancy test is worth doing but the result may not be conclusive. It will depend on how concentrated the urine is and the level of hormone in the blood which varies between women. Sometimes there is a risk of implanted pregnancy but it is too early for a pregnancy test to detect it. If there is any previous risk of pregnancy as well as any risks within the 96 hours leading up to the request, levonorgesterel can be considered as it may reduce the more recent pregnancy risk and there is no evidence to suggest the levonorgesterel EC will have any teratogenic effect.

Q Are there any restrictions to use for medical reasons?

A There are no medical restrictions to the use of levonorgesterel EC. Even if taken when there is already an implanted pregnancy there is no evidence to suggest the levonorgesterel EC will have any teratogenic effect.

The manufacturers of ulipristal suggest it should not be used in women who have severe asthma which is not controlled by oral glucocorticoids, those with hepatic dysfunction, hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption as well as those who have shown hypersensitivity to ulipristal. On a precautionary principle it is currently recommended that breastfeeding should be avoided for seven days after taking it8 and that ulipristal should not be repeated in the same cycle. Current evidence suggests there is no reason to believe that ulipristal will damage any ongoing pregnancy.

The medical eligibility criteria for a copper intrauterine devices insertion are the same as for any intrauterine device insertion except that heavy periods is not a problem as the copper intrauterine device does not need to be left in long-term if the bleeding is unacceptable. Young age, nulliparity, risk of STI or ectopic pregnancy history do not restrict choices for intrauterine device.9

Q Are there any relevant drug interactions?

A There are no relevant drug interactions with a copper intrauterine device.

Both levonorgesterel and ulipristal are affected by liver enzyme inducing drugs. No studies have been done but, on a purely pragmatic basis, national guidance suggests that a double dose of levonorgesterel can be used if a copper intrauterine device is unacceptable for the woman taking enzyme inducing drugs. However it does not currently support the doubling of dose for ulipristal.

Ulipristal has a theoretical risk of interaction with hormonal contraception as it is a progesterone  receptor modulator which has led to national guidance suggesting an extra seven days’ precaution when starting these methods immediately after ulipristal,7 compared to levonorgesterel.

For the second part in this series, follow this link


1. World Health Organisation. Emergency Contraception Fact Sheet 244 July 2012 accessed 22/1/2015
2. Faculty of Sexual and Reproductive Health. Clinical guidance Emergency Contraception 2012 accessed 22/1/2015
3. Wilcox AJ, Dunson D, Baird DD. The timing of the “fertile window” in the menstrual cycle: day specific estimates from a prospective study, Br Med J; 2000:321:1259
4. Espinos JJ, Rodriguez-Espinosa J, Senosiain R et al. The role of matching menstrual data with hormonal measurements in evaluating effectiveness of post coital contraception. Contraception; 1999:60:243-7
5. Stirling A, Glasier A Estimating the efficacy of emergency contraception – how good are the data. Contraception; 2002:66:19-22
6. Brache V, Cochon L, Deniaud M, Croxatto H. Ulipristal acetate prevents ovulation more effectively than levonorgestrel: analysis of pooled data from three randomized trials of emergency contraception regimens. Contraception; 2013:88:611-618
7. Faculty of Sexual and Reproductive Health. Clinical guidance Quick starting contraception. 2010 accessed 22/1/2015
8. Faculty of Sexual and Reproductive Health. Ulipristal in Breast Feeding women –Update 2013
9. Faculty of Sexual and Reproductive Health. Clinical guidance Intrauterine Contraception 2007 accessed 22/1/201