IUD contraception linked to lower cervical cancer risk

"IUDs [intrauterine contraceptive devices] may cut the risk of cervical cancer by a third," reports The Guardian. This was the finding of research combining the results of studies, mainly from developing countries, that investigated the risk of cervical cancer in women using an IUD (also known as the coil).

Cervical cancer is the third most common cancer worldwide but only the 13th most common in women in the UK. This is due in part to the national cervical screening programme and the more recent human papillomavirus virus (HPV) vaccination programme – HPV causes at least 70% cervical cancer cases.

The research found that women from around the world who had ever used an IUD had a reduced risk of cervical cancer compared with those who hadn't used one, but it's not clear whether this would be true in the UK. There could have been other reasons for the results that were specific to the individual countries where the studies were carried out – a mix of developed nations, such as Spain, and developing nations, such as Kenya.

The researchers speculated that an IUD may have some effect on the tissue of the cervix that reduces the risk of HPV infection.

The IUD remains the most effective contraceptive, but it doesn't protect against sexually transmitted infections. The best ways to reduce your risk of cervical cancer are to have the HPV vaccine if you are between 12 and 18 years old, stop smoking and attend cervical screening appointments.

Read more about cervical cancer prevention.

Where did the story come from?

The study was carried out by researchers at the University of Southern California. It was supported by the Department of Obstetrics and Gynecology at the University of Southern California, and a National Cancer Institute grant. It was published in the peer-reviewed journal Obstetrics & Gynecology.

The review prompted different headlines in the media. While The Guardian correctly reported that more research is needed to understand how IUDs work to protect against cancer, the Mail Online said "very strong evidence" was found that the IUD coil protects against cervical cancer and that the analysis "could not find any other reason" for this association.

This is inaccurate. In fact, there were "other reasons" discussed in the study that could have affected the results, including the type of IUD (hormonal or copper), the woman's age at the time of having the IUD and how long the IUD was used for.

The Guardian's report was the only one that suggested the review might be most relevant for women in low-income and developing countries, where access to cervical screening and prevention is likely to be limited.

What kind of research was this?

This was a systematic review and meta-analysis of studies looking at the use of an IUD and the incidence of cervical cancer.

A meta-analysis aims to pool the results of relevant studies to increase the number of participants and see if the findings are similar. When the studies report consistent findings – in this case, a link between having an IUD and the risk of cervical cancer – a common association can be identified. However, the pooled analysis is only clinically useful if the underlying studies are high quality.

As randomised controlled trials would be unethical when looking at the risk of cervical cancer, this review was mostly based on case-control studies. Women who developed cervical cancer were matched for a number of factors – such as age, ethnicity and sexual history – with a control group of women who did not develop it.

Case-control studies are useful when little is known about the effect of an intervention on a disease, but they are not able to show cause and effect.

What did the research involve?

The researchers searched online medical databases for studies looking at whether women who had and had not used an IUD developed cervical cancer.

A total of 16 studies had a strong enough design to be included in the pooled analysis. The studies included 4,945 women who developed cervical cancer and 7,537 who did not. Five studies were in developed countries and the remaining 11 in developing countries.

The analysis took into account the following potential confounding factors, where available:

• socio-economic status
• smoking history
• age they started to have sex
• number of sexual partners
• whether or not they had HPV (the infection is linked to at least 70% of cervical cancer cases)
• number of cervical smear tests
• number of pregnancies

What were the basic results?

Women who had used an IUD were 36% less likely to develop cervical cancer (odds ratio 0.64, 95% confidence interval 0.53 to 0.77).

This finding held true even when confounding risk factors were taken into account.

How did the researchers interpret the results?

The researchers said the meta-analysis revealed "a robust and inverse association between any use of a contraceptive coil [IUD] and incident[s of] cancer with the overall incidence approximately 30% lower in women who reported ever using the device."

But they also noted that, because contributing studies were completed before an HPV vaccine was available, "the magnitude of this association may be most relevant to populations in which women 30 years of age and older remain largely unvaccinated".

Conclusion

This systematic review and meta-analysis suggests that any previous use of an IUD reduces the risk of cervical cancer. However, it has limitations that make the findings less generalisable to the UK population.

Firstly, none of the women had received an HPV vaccine. As HPV causes the majority of cases of cervical cancer in the UK, the NHS has offered the HPV vaccine to girls aged 12 to 18 since 2008. This means that a lower proportion of women in the UK will be at risk of cervical cancer. The protective effects of an IUD may therefore be greater in populations that have higher cervical cancer risk. Women in developed countries are not only more likely to have had the HPV vaccine, but they are also more likely to have better access to healthcare and have had regular cervical cancer screening. The study results are therefore likely to be more relevant to women in developing countries.

Secondly, the study was not able to investigate associations between the type of IUD (hormonal or copper), the duration of use, age when the IUD was fitted or access to preventative healthcare. Omitting age at fitting is also problematic because the World Health Organization has found that age is a highly influential factor in HPV prevalence: the earlier a woman has the coil fitted, the greater the protection against HPV infection she may get.

Thirdly, although there were 12,482 women in the analysis, the figures become quite small when broken down into specific risk factors or subgroups of women. Many of the studies, for example, did not include HIV status or family history of cervical cancer, both of which raise the risk of cervical cancer.

An IUD is a safe and effective form of contraception, but using one offers no guarantee against cervical cancer. It's advised that you have the HPV vaccine if offered it and attend screening appointments when invited.

An IUD will also not protect you against sexually transmitted infections. For that, you need a barrier form of contraception, such as condoms.