THE WHO PUBLISHES RESEARCH FINDING ON ORAL CONTRACEPTIVES AND RISK OF VENOUS THROMBOEMBOLISM
Press Release
H/2889
THE WHO PUBLISHES RESEARCH FINDING ON ORAL CONTRACEPTIVES AND RISK OF VENOUS THROMBOEMBOLISM
19951214 ADVANCE RELEASE The 16 December issue of the medical journal The Lancet carries two World Health Organization (WHO) papers on the risk of deep venous thromboembolism (VTE) -- that is, formation of blood clots in veins -- in women using combined oral contraceptives (that is, pills that contain both an estrogen and progestogen).These papers provide the first published observation that oral contraceptive pills containing the newer progestogens, desogestrel and gestodene, may double the risk of VTE compared with pills that contain the older progestogens, levonorgestrel and norethindrone.
"In the light of the attention this issue has received in the press over the last few weeks, the publication of these papers is significant. The data will greatly help researchers and health practitioners to evaluate the risk of thromboembolism from oral contraceptives and enable them to give sound advice on contraceptive choices", says Dr. Giuseppe Benagiano, Director of the United Nations Development Programme (UNDP)/United Nations Population Fund (UNFPA)/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), which organized and financed the study.
The principal findings reported in the two papers are as follows:
-- The overall risk of VTE associated with oral contraceptives is in the lower range of the risk levels reported in previous studies.
-- Women with a high body weight or those with a history of high blood pressure in pregnancy are at a slightly higher risk of VTE compared with women who do not have these problems. In the WHO study, history of hypertension or smoking habit did not alter the risk.
-- Increase in the risk of VTE becomes apparent within the first months of starting the use of combined oral contraceptives and disappears within a few months of stopping their use.
-- Users of combined pills that contain the new progestogens, desogestrel or gestodene, may be at double the risk of VTE compared with users of pills that contain the older progestogens, levonorgestrel and
norathindrone. This finding was quite unexpected as the two new progestogens were thought to be safer than the older progestogens with regard to the risk of cardiovascular disease.
-- It was estimated that in the United Kingdom three to four cases of VTE could be expected per year among 100,00 apparently healthy women of reproductive age who do not use oral contraceptives. Among women using pills containing levonorgestrel or norethindrone about 10 cases of VTE would be expected per 100,000 per year, whereas 20 cases of VTE would occur among those who are using pills containing desogestrel or gestodene.
The two papers published today are the first to result from a large epidemiological study coordinated on behalf of HRP by the Department of Epidemiology and Public Health, University College, London Medical School, London.
This hospital-based case-control study was conducted in 21 centres in 17 countries in Africa, Asia, Europe and Latin America. Its main aim was to determine if there was an association between currently available hormonal contraceptives and cardiovascular disease. A total of about 3,800 cases of stroke, VTE and myocardial infarction and some 11,200 matched controls took part in the study. The number of cases in the VTE group was 1,143 with 2,998 matched controls.
Prior to publication, a summary of the results on VTE was made available to national drug regulatory authorities. Health authorities in some countries have already taken steps they consider appropriate and have informed health care providers and users about the risks associated with desogestrel and gestodene.
As stated in the WHO press release of 20 October (WHO/77), the risk of VTE should be interpreted keeping in mind that the incidence of venous thromboembolism in women of reproductive age throughout the world is low, and that any excess risk from using oral contraceptives affects a relatively small number of women. The additional risk associated with brands containing desogestrel or gestodene has been estimated to be 10 cases per year in 100,000 users over and above that observed among users of pills containing levonorgestrel or norethindrone.
"Even though the use of oral contraceptive pills increase the risk of deep venous thromboembolism by some three to four times, the condition remains a rare event affecting only a very small number of women taking the pill. In fact, pregnancy, prolonged bad rest or immobilization, and recent surgery carry a greater risk of venous thromboembolism than oral contraceptive use", said Dr. Neil Poulter of University College, of the London Medical School who coordinated the study.
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Dr. Olav Meirik, Chief of the HRP Unit of Epidemiological Research says that, "The WHO findings are supported by other independent studies published in the same issue of the journal The Lancet. Thus it appears unlikely that these results are due to chance or bias. It will be important to conduct further research to improve our understanding of the biological mechanisms responsible for the elevated risk of venous thromboembolism."
Background of HRP
The Special Programme of Research, Development and Research Training in Human Reproduction was established by the WHO in 1972 to coordinate, promote, conduct and evaluate international research in human reproduction. The Programme brings together health care providers, policy makers, scientists, clinicians and the community to identify priorities for research and for the strengthening, in developing countries, of research institutions. It marshals the scientific community to conduct research in human reproduction and to evaluate the results of such research. The Programme also ensures coordination of efforts in this field and in the exchange of information, joint planning and joint activities among national, non-governmental and international agencies involved in institution strengthening and research in human reproduction and family planning. In May 1988, the UNDP, UNFPA and the World Bank joined WHO as co-sponsors of the Programme.
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