Emergency contraception: coil 99.9% effective

“The coil is a much more effective form of emergency contraception than the morning-after pill,” the Metro has reported. The coil, medically known as an intrauterine device or IUD, is often used as a form of long-term contraception, but it can also be implanted after sex to provide emergency protection against pregnancy.

IUDs are in the news as researchers have today published findings on how effectively they prevent pregnancy in women who have them implanted after unprotected sex. Drawing on data from 43 previous studies, the review found women who had an IUD fitted after having unprotected sex had a pregnancy rate of 0.09% – the equivalent of less than 1 pregnancy out of every 1,000 IUDs inserted. Another way of saying this is that 99.91% of women who used an IUD as emergency contraception did not become pregnant.

The study was mainly based on findings relating to IUDs containing copper, rather than all-plastic devices, and the data came largely from Chinese studies. As a consequence, the results may not reflect the effectiveness of other types of coil or use of the IUD in the UK. Also, the research did not directly compare the coil to the effectiveness of emergency contraceptive pills, or examine how easily women could obtain an emergency coil following unprotected sex. These will both be important factors for women deciding which option to use.

Where did the story come from?

The study was led by researchers from the University of Princeton USA in collaboration with researchers based in South Africa, China and the UK. It was funded by a grant from Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the researchers declared that they had no conflicts of interest.

The study was published in the peer-reviewed medical journal Human Reproduction.

Some news coverage of this research suggested women should “forget morning-after pills” as a form of emergency contraception, which is somewhat irresponsible as they remain an effective form of emergency contraception for some women. Also, emergency contraceptive pills may be a more practical and accessible option at times.

Women seeking emergency contraception should be informed about the full range of options available to them to help them make a decision about the most appropriate method for them.

What kind of research was this?

This research was a systematic review investigating how effective intrauterine devices are at preventing pregnancy when used for emergency contraception.

An intrauterine device (IUD) or ‘the coil’ is a form of birth control that is placed in the uterus of a woman to prevent pregnancy. An IUD is made of copper and plastic and works by physically preventing sperm from fertilising the egg. They can also prevent any fertilised eggs from implanting in the womb. Some devices, known as intrauterine systems, also release hormones that prevent fertilisation, but these were not included in this review and are not recommended for emergency contraception.

A systematic review seeks to identify and summarise all known literature published on a specific topic. It is an effective way of summarising a large body of research to answer a specific research question.

It should also be noted that the study did not directly compare the use of IUDs with the use of the morning after pill, nor did it compare how easily women could access either option after unprotected sex. This means we cannot tell which is a more viable option for women seeking emergency contraception, or say that one is intrinsically ‘better’ than the other based on the study’s results alone.

What did the research involve?

The researchers performed searches of research databases to gather all relevant published studies on women being given an IUD after seeking emergency contraception.

Studies were only included if clear information was available on whether the emergency contraception was effective and whether or not the women became pregnant. Only studies published in English or Chinese were included. The authors state that research published in Chinese was included because there is a high volume of contraceptive research taking place in China.

Those studies that met the inclusion criteria were analysed in more detail and data were extracted from them by two reviewers working independently of one another, which is intended to reduce errors and bias during data selection. The authors then described the results from the individual studies.

The researchers then used a simple method to pool the results of the different studies. During this process they combined the number of women seeking contraception and the number who became pregnant from across all the studies, which was intended to estimate the overall effectiveness of IUDs at preventing pregnancy.

What were the basic results?

The researchers included 42 studies that provided data on the effectiveness of IUDs in women seeking emergency contraception. These represented studies conducted in six countries between 1979 and 2011, and included 7,034 women using eight different types of IUD. Nearly all the IUDs were devices containing small amounts of copper, and only a small number of plastic-only IUDs were included, in the older pre-1985 studies. Most of the study data came from research based in China.

The main finding was that, out of the total 7,034 IUD insertions after unprotected sex, there were 10 recorded pregnancies. This gave a combined IUD failure rate (failure to prevent pregnancy) of 0.14% (95% CI 0.08 to 0.25%).

The authors commented that a study in Egypt gave a “surprisingly high” failure rate of 2%, which was vastly different from all the other studies. If this single atypical study was excluded the combined failure rate of using an IUD fell to 0.09% (95%CI 0.04 to 0.19%).

This rate means that less than one woman in every 1,000 would fall pregnant using the IUD as an emergency contraceptive. Another way of saying this is that 99.91% of women who used an IUD as emergency contraception did not become pregnant.

The maximum length of time from intercourse to IUD insertion ranged from two days to 10 or more days. Most of the insertions (74% of the studies) occurred within five days of intercourse. However, the studies did not include sufficient detail about the delay between intercourse and insertion of IUD for the researchers to analyse accurately how the effectiveness of the IUD was affected by any delay.

How did the researchers interpret the results?

The researchers conclude that “IUDs are a highly effective method of emergency contraception, with a failure rate of less than one per thousand”.

In discussing the different types of IUD they concluded that use of a copper IUD “is by far the most effective emergency contraception option” compared with the non-copper alternatives.


This systematic review of IUD use in emergency contraception provides useful estimates of pregnancy rates following insertion after unprotected sex. To assess the issue it drew upon studies in several different countries, although the studies were primarily carried out in China. The results of the study suggest that IUDs are a highly effective form of emergency contraception, with a very low failure rate of around 0.09%.

It should be noted that the research primarily estimates how likely it is that a woman would become pregnant after having unprotected sex and having an IUD fitted. It does not, however, tell us important related factors such as how available IUDs are after unprotected sex, nor does it confirm that they are necessarily a better option than emergency contraceptive pills. For example, women can obtain emergency contraceptive pills from specially trained pharmacists, whereas an IUD needs to be fitted by a trained clinician. This is not to say that either is better or more practical, rather that there are particular considerations to take into account with each form or contraception beyond overall failure rate.

The research also has some limitations, which should be considered when interpreting the results. For example, most of the results included in the review related to the copper coil and some were older devices, so the overall failure rate of 0.09% may not accurately represent the failure rate of newer IUDs or ones that contain hormones (known as intrauterine systems). More data on these devices are needed to establish whether they have a similar failure rate leading to pregnancy as the copper options included in the review. Similarly, most of the data feeding into the 0.09% figure come from studies based in China. Hence, this overall estimate best reflects copper IUD use in Chinese women. The effectiveness in other countries and for other IUDs is less certain based on this study alone.

Also, the research originally set out to assess the effectiveness of IUDs in detail so the researchers could see how many days had elapsed between unprotected sex and insertion of the IUD. However, the studies they identified did not contain sufficient detail for this to be possible. Hence, the combined IUD failure rate represents all cases together regardless of the time between intercourse and insertion of IUD. It is likely that the time between unprotected sex and insertion of the IUD directly influences the effectiveness of the contraceptive device, but this review was unable to analyse this. The recommended maximum interval after unprotected sex is 120 hours (five days) for most currently marketed devices.

As research was restricted to studies published in English or Chinese, this will exclude potentially informative research in other languages. The results of these excluded studies may have influenced the conclusions of this review had they been included.

When discussing their research the authors highlight recent studies exploring attitudes towards IUDs, which identified several potential barriers to a greater use of IUDs as emergency contraception. These included the waiting time (not being able to get a coil on the day emergency contraception is requested), low levels of awareness and understanding among patients, and a lack of understanding among healthcare providers. The results of this study, which show that IUDs are a highly effective option, may renew efforts to increase awareness of IUDs as an emergency contraceptive option. On this note, a spokeswoman for the Family Planning Association is quoted in the Metro as calling for more women to be offered the IUD routinely as a method of contraception.

The Metro’s headline suggesting that women should “forget morning-after pills” is somewhat irresponsible, as morning after pills remain an acceptable and effective method of emergency contraception for some women. A previous systematic review carried out by the Cochrane collaboration in 2008 concluded that drugs (such as the morning after pill) and copper IUDs were both effective and safe methods of emergency contraception.

The risks of sexually transmitted diseases associated with unprotected sex are well known and the coil, whether used as a standard contraceptive or an emergency contraceptive, does not reduce these risks.

NHS Attribution