Admission for and mortality from primary venous thromboembolism in women of fertile age in Denmark, 1977-95.

Epidemiological studies indicate that use of third generation oral contraceptives increases the risk of venous thromboembolism more than does use of second generation oral contraceptives. Critics have suggested that this finding may be confounded by indication, since third generation pills were considered to be safer and were therefore perhaps prescribed more often to women at high risk. If confounding by indication is the only explanation for the observed association, the incidence of venous thromboembolism in the population should not have changed when prescribing patterns changed from second generation to third generation pills with no increase in overall use of oral contraceptives. Vandenbroucke et al and Thomas reported increasing mortality from venous thromboembolism among young women in the Netherlands and in England and Wales from the mid-1980s to the 1990s, when the use of third generation pills was increasing. 5 Since mortality from venous thromboembolism depends on both aetiological and prognostic factors, however, it may be more appropriate to look at incidence. In Denmark, roughly a quarter of women aged 15-44 used oral contraceptives during the 1980s and the beginning of the 1990s. The first third generation oral contraceptive, containing desogestrel, was released in 1984, and the third generation preparations containing gestodene and norgestimate were introduced in 1988 and 1990, respectively. Use of third generation pills represented 0.2% of the total use of oral contraceptives in 1984, 17% in 1988, 40% in 1990, and 66% in 1993.