Abstract
The risk of venous thrombosis (VT) varies according to the type of progestogen that
is found in combined oral contraceptives (COCs). When combined with the estrogen component
ethinylestradiol (EE), the androgenic progestogens are better able to counteract the
EE-induced stimulation of liver proteins and hence are associated with a twofold decreased
risk of VT compared with non- or antiandrogenic progestogens, which exert limited
counteraction of EE. Because EE is responsible for the increased risk, novel estrogens
such as estradiol were developed and seem to have a lower risk of VT than EE. Besides
COCs, there are other methods of hormonal contraceptives, such as progestogen-only
contraceptives, which do not increase VT risk, except for injectables. Other nonoral
contraceptives are combined vaginal rings and patches. There is insufficient evidence
regarding the risk of VT associated with these two methods compared with COCs. The
increased risk associated with COCs is more pronounced in women with inherited thrombophilia.
In these women, the progestogen levonorgestrel seems to be associated with the lowest
risk of VT. Currently, there are no studies that have investigated the risk of VT
in women who switch COCs. We hypothesize that switching COCs, even when switching
from a high- to a low-risk COC, increases the risk of VT. Finally, risk prediction
models in women who use COCs are lacking. Since there is a large number of VT cases
associated with COC use, it is important to identify women at risk of VT and advise
them on alternative contraception methods.
Keywords
contraceptives - oral - combined oral contraceptives - thrombosis - risk
