Most refined analysis to date confirms link between third-generation pills and venous thromboembolism.

In Britain use of oral contraceptives containing a "third generation" progestogen is associated with a higher risk of venous thromboembolism than use of pills containing levonorgestrel. Hence the investigators conducted a cohort analysis to compare the risk of venous thromboembolism in the periods leading up to the pill scare between January 1993 and December 1999. They also conducted a case control analysis to compare the risks associated with the different types of pills. In these analyses women taking third-generation pills had twice the odds of venous thromboembolism of those using pills containing levonorgestrel. It is noted that the difference between the results in the cohort and case control analyses is attributable to the additional adjustments for confounding factors in the latter. The results were similar in the years preceding the pill scare and immediately thereafter.