Oral contraceptive/clot link rears its head again

Women taking third-generation oral contraceptives (ie those containingdesogestrel or gestodene as the progestin component) have a 1.7-fold increased risk of venous thrombosis compared with those taking second-generation products, according to a study in the British Medical Journal, which could stoke the fires of a debate first ignited several years ago (Marketletters passim). The authors conclude that, although the risks are small, they should be considered when selecting which OC product to use.

Researchers at the University Medical Centre Utrecht in the Netherlands pooled the results of studies assessing risk of venous clotting among women using OCs 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 OCs, which may have affected the results of later studies.

Previous trials linking third-generation OCs 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 of the new report, "the biases were not large enough to account for the observed results in our analysis."