From the available evidence, the most convincing evidence relates to a greater risk in the 1st year of use than in subsequent years and a lack of continuing risk in those who have stopped HRT. Although requiring confirmation in larger studies, it also seems likely that there is a substantially lesser risk with transdermal compared with oral preparations and that the overall VTE risk with combination preparations may be influenced by the type of progestogen used.
There is some evidence that the effect of estrogen therapy may be dose related, with no significant VTE risk associated with doses of oral estrogen of around 0.3 mg.
As discussed above, the available evidence suggests that transdermal preparations are associated with a substantially lower risk of VTE than oral preparations.
How should HRT be managed in those with a previous VTE? A personal history of thrombosis is a contraindication to oral HRT. If it is considered that quality of life is so severely affected that the benefits of HRT outweigh the risks, a transdermal preparation should be used.
Where HRT is to be used in those with prior VTE, prophylactic anticoagulant therapy may be considered while the woman is taking HRT.
If it is considered desirable that a woman should continue HRT after a VTE has occurred on therapy, she should be referred to a clinician with special expertise in managing women at increased thrombotic risk requiring HRT.
As further VTE may be prevented by anticoagulation, consideration can be given to postponing the withdrawal of HRT until the woman is due to stop anticoagulant therapy for her VTE.