The Mail
London, UK
Published: 7 January, 2007
Obese women who take the Pill are five times more likely to develop life-threatening blood clots, research suggests.
The additional risk is much higher than previously thought and could lead to a tightening of guidelines for prescribing oral contraceptives.
At present, women can be given an oestrogen-based contraceptive even if they have a Body Mass Index (BMI) between 30 - the point at which they are classified as obese - and 35.
But the findings of the European Active Surveillance (EURAS) Study, which looked at women from seven countries including Britain, suggest the risk of developing blood clots increases dramatically for such women.
One in four women are classed as obese - so fat it threatens their health - with rates predicted to rise to 70 per cent within a decade. Around 3.5million women use oral contraception, with the majority taking a combined pill containing both oestrogen and progestogen.
The EURAS study looked at 59,000 women over a number of years. The calculations were done after adding all the years of all the women together in order to make the measurement more precise.
The results showed that for every 100,000 years of women not using the Pill there were 44 cases of blood clots. The figure rose to 90 cases when narrowed down to women using the combined Pill.
But when the study looked just at women taking the Pill with a BMI over 30, it found 230 cases - five times the risk of those not on the Pill. The results are reported today in the Journal of Family Planning and Reproductive Health Care.
The link between venous thromboembolism (VTE) and the Pill has been known for more than 15 years.
The increased risk in obese women comes from the extra oestrogen they naturally have.
Those not on the Pill also run a risk of blood clots, although earlier studies had lower estimates than the EURAS research.
Between one and two women in 100 who develop the condition die when a clot moves from a leg to the lungs and blocks the air supply.
Current guidelines from the Faculty of Family Planning warn against prescribing the combined Pill to women with a BMI over 35.
Dr Anne Szarewski, editor-in-chief of the Journal of Family Planning and
Reproductive Health Care, said it was likely guidelines would be tightened.
She said: 'This study is important because it shows the absolute risk of VTE for women who are obese and taking the combined Pill is high.
'We have known that obesity is a risk factor but it was previously assumed the absolute risk was quite low compared with women not taking the Pill, but these findings show it's five times higher.
'Obesity is clearly the most important risk factor for VTE and these findings have extended the danger zone.' Dr Szarewski, of the Margaret Pyke Centre in London, said she stopped prescribing the Pill to women with a BMI over 30 when preliminary results from the EURAS study two years ago suggested it was risky. She said: 'A lot of women are upset but if you explain the reasons they understand because VTE is a side effect that can be fatal.
'It gives obese women an incentive to lose weight, although they can safely take progestogen-only pills that do not contain oestrogen and use barrier methods.'
Dr Toni Belfield, director of information at the fpa - formerly Family Planning Association - said the EURAS data would be used to update the guidelines once it was published in full later this year.
She said: 'Women who are obese should not be prescribed oestrogencontaining Pills but other forms of effective contraception.
'When women get family planning advice, they are always asked about blood pressure and BMI.
'This study shows that we do have safe Pills, but we don't always have safe women,' she added.
Doctors use the BMI system to assess whether patients are overweight. To calculate it you divide your weight in kilos by your height in metres squared. Anything under 25 is fine, while a BMI over 30 is defined as obese.
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Pill health risk is five times higher for obese women
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