Women taking third generation oral contraceptives have a 1.7 fold increased risk of venous clotting (thrombosis) compared with those taking second generation oral contraceptives, concludes a study in this week's BMJ. Although the risks are small, they should be considered when deciding which contraceptive pill to use, report the authors.
Researchers at the University Medical Centre Utrecht in the Netherlands pooled the results of studies assessing risk of venous clotting among women using oral contraceptives before October 1995. The team chose October 1995 as the end date because at that time four studies were published highlighting the possible risk of third generation pills, which may have affected the results of later studies. A sensitivity analysis was applied to the results of each study to ensure an accurate estimate of overall risk.
Previous trials linking third generation oral contraceptives to venous thrombosis have been vigorously debated, with suggestions that flaws in the design and analysis of the studies can explain their findings. Although bias can never be excluded with certainty in some studies, say the authors, the biases were not large enough to account for the observed results in our analysis.
Linda Minnen or Marjan Wolters, Public Relations, University Medical Center Utrecht, Utrecht, The Netherlands.
Third generation oral contraceptives and risk of venous thrombosis: meta-analysis BMJ Volume 323, pp 131-134
Editorial: The third generation pill controversy ("continued") BMJ Volume 323, pp 119-120