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Contraceptive patches and vaginal rings ‘double thrombosis risk’

GPs have been advised to switch patients from contraceptive patches and vaginal rings as a study shows they double the risk of venous thrombosis in women when compared with oral contraception.

In the first study to look at the risk of VTEs for transdermal patches, the researchers found it was eight times the increased risk compared with those not taking contraception.

The researchers found women who used vaginal rings had 6.5 times the VTE risk of those who did not take contraception.

Experts warned the ‘extremely concerning' study results could undo years of work reducing teenage pregnancies, but the authors urged GPs to use oral levonorgestrel or norgestimate- based contraceptives to reduce the risk of VTEs.

The Danish researchers looked at a cohort of 1,626,000 women aged 15 to 49 years from national registries that were free from thrombotic risk at baseline.

After nine years, transdermal patches were associated with an adjusted relative risk of 2.3 and the vaginal ring was associated with a risk of 1.9, compared with users of oral contraceptives containing levonorgestrel.

The incidence of confirmed VTEs was 4.52, 6.22, 7.75 and 9.71 events per 10,000 exposure years, for oral contraception containing norgestimate, oral contraception containing levonorgestrel and oestrogen, rings and patches.

When length of use was analysed more closely, the relative risk of venous thrombosis in women using combined oral contraceptives was reduced with increasing length of use by almost 50%, while no changes in relative risk over time were observed for patches or vaginal rings.

Study lead Dr Ojvind Lidegaard, professor of obstetrics and gynaecology at the University of Copenhagen, said: ‘A risk of 10 per 10,000 person years implies a risk of venous thrombosis of more than 1% over a 10-year user period.

‘Therefore, women should generally be advised to use combined oral contraceptives with levonorgestrel or norgestimate.'

Dr Anne Connolly, a GPSI in gynaecology in Bradford and chair of the Primary Care Women's Health Forum, said the study was ‘extremely concerning' and did not take into account the risk factors for VTEs

She said: ‘If commissioners and prescribing advisors make knee-jerk decisions based on poor studies such as this one we will be reduced to providing a range of cheaper, older, less well tolerated options to women and we are likely to see unplanned pregnancy rates increasing again.'

 

But Dr Fiona Cornish, a GP in Cambridge and president-elect of the Medical Women's Forum, said the study confirmed the current best practice: ‘We hardly use patches and rings as they are much more expensive than COCs.

 

‘What is important is that GPs and nurses continue to advise the use of COCs in preference where possible.'

 

Dr Richard Ma, a GP in Holloway, north London, and London sexual health champion, agreed with the study findings, but warned: ‘It must be stressed that the absolute risk of any VTE events in women using these methods are still small and the risk is increased in pregnancy.'

BMJ 2012, published online 10 May

http://bmjopen.bmj.com/content/2/3/e000851.abstract?ct

 

VTE relative risk, compared with non-users

COC with levonorgestrel and oestrogen             2.37

COC with norgestimate            2.63

Patch                                         4.40

Vaginal ring                                4.29

Levonorgestrel IUS                 0.80

 

BMJ 2012, published online 10 May

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