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26 October 2011
A study published on bmj.com has confirmed previous findings that certain oral contraceptive pills are more likely to cause serious blood clots.
The authors, led by Dr Øjvind Lidegaard from the University of Copenhagen, have found that women on pills containing one of the newer types of progestogen hormone (drospirenone, desogestrel or gestodene) have double the risk of venous thromboembolism (VTE) than women on pills containing an older progestogen (levonorgestrel).
They reviewed data of the hormonal contraception patterns and first time VTE episodes for all Danish non-pregnant women between the ages of 15 and 49 from January 2001 until December 2009. The participants had no previous record of either blood clots or cancer before the study began.
In total, the research team assessed over eight million women years of observation and found that, during this period, there were 4,246 first episodes of VTE.
The relative risk of VTE whilst taking the oral contraceptive pill is still low. However, compared with non-users of hormonal contraception, pills with levonorgestrel increase the risk of VTE threefold and pills with drospirenone, desogestrel or gestodene increase the risk sixfold.
In absolute terms, the risk of VTE in current users of newer pills is about 10 per 10,000 women years. According to the authors, this means that about 2,000 women should shift from using oral contraceptives with desogestrel, gestodene, or drospirenone to those with levonorgestrel to prevent one event of VTE in one year.
They also concluded that the increased risk remained even after taking account of other possible causes for VTE.