Progress in Reproductive Health Research |
Making Informed Choices About Combined Oral Contraceptives
Any assessment of the risk of cardiovascular disease associated with combined oral contraceptives is complex. Nevertheless, it is clear that mortality rates from cardiovascular disease are extremely low among women of reproductive age, and that the added risk of using steroid contraceptives is also very low. Within the context of the everyday risks of modern life, steroid contraceptives are safe. Factors which need to be taken into account when determining a woman's risk of cardiovascular disease while using combined oral contraceptives include:
the age-specific incidence of each cardiovascular condition;
the strength of the association between use of combined oral contraceptives and each cardiovascular outcome;
the woman's age and presence of other risk factors for cardiovascular disease such as smoking and a history of hypertension;
whether there are important differences in risk between particular formulations of combined oral contraceptive and, if so, the choice of formulation.
At the population level, the impact of combined oral contraceptives on cardiovascular disease within any country depends on:
the age-specific prevalence of use of combined oral contraceptives;
the characteristics of the users;
if there are important differences between formulations, the proportion of women using each formulation at different ages.
The number of cardiovascular events attributable to the use of combined oral contraceptives is very small, especially among users of all ages who do not smoke and among younger users who smoke. The number of associated deaths is even smaller and, again, is highly dependent on whether the user is a smoker. Any small increase in risk of cardiovascular disease must be considered against the very high contraceptive efficacy of combined oral contraceptives and the rapid reversibility of this effect after they are stopped. The use of less reliable alternative methods of contraception (or the avoidance of any contraception) exposes women to an increased risk of pregnancy, a condition which is associated with a higher incidence of venous thromboembolic disease than that associated with the use of any of the currently available low-dose combined oral contraceptives. In addition, combined oral contraceptives are associated with many non-contraceptive benefits, including a reduced risk of endometrial and ovarian cancer. By any standards, all of the currently available low-dose combined oral contraceptives can be regarded as safe.
The Study Group concluded that:
The incidence and mortality rates of all cardiovascular diseases (stroke, acute myocardial infarction and venous thromboembolic disease) in women of reproductive age are very low.
Any increase in incidence of or mortality from cardiovascular disease attributable to use of combined oral contraception is very small if users do not smoke and do not have other risk factors for cardiovascular disease. For example, among users of combined oral contraceptives who do not have risk factors for cardiovascular disease, the annual risk of death attributable to use of oral contraceptives is approximately 2 deaths per million users at 20–24 years of age, 2–5 per million users at 30–34 years of age and approximately 20–25 per million users at 40–44 years of age.
The risk of mortality from cardiovascular disease attributable to use of oral contraception is much greater (up to 10-fold) among women aged 40–44 years than among women aged 20–24 years.
At any given age, a woman who smokes but who does not use oral contraceptives is at greater risk of death from arterial disease than a user of oral contraceptives who does not smoke.
The benefits of blood-pressure measurement in reducing the risk of cardiovascular disease attributable to use of oral contraception increase with the age of the user.
Venous thromboembolic disease is the most common cardiovascular event among users of oral contraceptives. However, it contributes very little to any increase in the number of deaths since the associated mortality is relatively low compared with that associated with arterial diseases. Long-term disability from non-fatal venous thromboembolic disease is also low.
Estimated number of cardiovascular events at different ages among non-users and users of combined oral contraceptives in developed countries, by smoking habits.
Non-smokers—Non-users
Number of events (per million
woman–years)Age (years)
20–24
30–34
40–44
Acute myocardial infarction
0.13
1.69
21.28
Ischaemic stroke
6.03
9.84
16.05
Haemorrhagic stroke
12.73
24.28
46.30
Venous thromboembolism
32.23
45.75
59.28
Total 51.12
81.56
142.9
Non-smokers—Users*
Number of events (per million woman–years)
Age (years)
20–24
30–34
40–44
Acute myocardial infarction
0.20
2.55
31.92
Ischaemic stroke
9.04
14.75
24.07
Haemorrhagic stroke
12.73
24.28
92.60
Venous thromboembolism
96.68
137.3
177.8
Total
118.7
178.9
326.4
Smokers—Non-users
Number of events (per million woman–years)
Age (years)
20–24
30–34
40–44
Acute myocardial infarction
1.08
13.58
170.2
Ischaemic stroke
12.06
19.67
32.09
Haemorrhagic stroke
25.46
48.55
138.9
Venous thromboembolism
32.23
45.75
59.28
Total
70.83
127.6
400.5
Smokers—Users*
Number of events (per million woman–years)
Age (years)
20–24
30–34
40–44
Acute myocardial infarction
1.62
20.36
255.3
Ischaemic stroke
18.09
29.51
48.14
Haemorrhagic stroke
38.19
72.83
231.5
Venous thromboembolism
96.68
137.3
177.8
Total
154.6
260.0
712.7
*Blood pressure was checked in users.