What is the relationship between the birth pill and thromboembolism (blood clots)?
Deep venous thrombosis and pulmonary embolism are uncommon if you are young (Figure 15.1). There is a slight increased risk of these problems if you are taking a combined oral contraceptive pill and the risk is further increased for those who are overweight or who smoke. The newer and lower oestrogen dose pills probably cause fewer problems. To put the risk in context, a woman taking the combined oral contraceptive pill is more likely to be hospitalised as a result of an accident than from a complication associated with her pill.
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Figure 15.1
A study by the World Health Organisation (WHO) published in 1995 provided evidence that the newer pills with their lower oestrogen content are associated with lower incidence of thromboembolism than the earlier higher oestrogen dose pills. This study also brought attention to the relationship between the progestogen in the combined oral contraceptive pill and thromboembolism.
There have been three “generations" of progestogens used in oral contraceptives. The WHO study found that the second generation progestogen, levonorgestrel, was only half as likely to be associated with thromboembolism compared to the third generation progestogens desogestrel and gestodene. Essentially, the WHO study demonstrated that the second generation progestogens were associated with a lower incidence of thromboembolism than had been previously believed. The third generation progestogens were not found to be associated with higher risks than anticipated.
In October 1995, the Committee on Safety of Medicines issued an alert to doctors and the media recommending that women taking third generation combined oral contraceptive pills should change to second generation preparations. The presentation of the information was such that many women were inappropriately led to believe that the combined oral contraceptive pill was associated with high risk of mortality. There was a 10,000 increase in the number of pregnancy terminations in the next nine months. Some Hospitals reported a 25% increase in births in July and August of 1996. There are risks of mortality with pregnancy termination and with childbirth. The emotional trauma of pregnancy termination is not easilyQuantified.
Table 15.1 puts the risk of deaths from thromboembolism in perspective.
Table 15. 1 Deaths per million women.
|
Risk |
Deaths per million women |
|
Second generation pill | approximately 2 |
|
Third generation pill | approximately 3 |
|
Pregnancy and childbirth | 60 |
|
Road traffic accidents | 80 |
|
Scuba diving | 220 |
|
Smoker (aged 35) | 1670 |
A change from a third generation pill to a second generation would be expected to prevent the death of one
women in every million taking the combined oral contraceptive pill. There are risks in most aspects of life. We cannot be complacent but every effort should be made to ensure that when clinical information is presented to the public, it is presented in perspective. One death in a million is a tiny risk but for any family (and doctor) involved it is a disaster of the most enormous proportion. There has been an indication that third generation progestogens may have been safer in relation to heart disease. The latest evaluation of the third generation of the combined oral contraceptive pill has concluded that these pills can be prescribed as a first choice preparation. There are a number of factors to be taken into account when assessing risk and the tiny risks involved probably make it virtually impossible to distinguish risks between second and third generation pills.
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