Doctors have noted that women using third generation birth control have a higher risk of thromboembolism. Now they know why.
New evidence shows that third generation contraceptive pills increases the body's resistance to the anticoagulant action of activated protein C (APC).
Researchers in the Netherlands conducted a small study to investigate whether the blood of women taking third generation pills is more resistant to APC. Compared with the second generation levonorgestrel, third generation desogestrel containing pills significantly increased the plasma resistance to this naturally occurring anticoagulant. As a result, women taking this form of the Pill are at increased risk of venous thromboembolism (Lancet, 1999; 354: 2036-40).