Hormones and pregnancy: thromboembolic risks for women

During their lifetimes, women face several unique situations with an increased risk of venous thromboembolism (VTE). Doctors in a variety of specialties must advise women on the risks of oral contraceptives (OC), hormone replacement or pregnancy. Modern 'low dose' OC are associated with a three to sixfold increased relative risk of VTE. Hormone replacement and selective oestrogen receptor modulators confer a similar two to fourfold increase in thrombotic risk. However, because the baseline incidence of thrombosis is higher in older postmenopausal women, the absolute risk is higher than in younger OC users. The risk of venous thrombosis is six to 10-fold higher during pregnancy than in non-pregnant women of similar age. Thrombophilic disorders increase the thrombotic risk of OC, hormone replacement and pregnancy, especially in women with homozygous or combined defects. This review focuses on recent data estimating the thrombotic risk of hormonal therapies and pregnancy in women with and without other thrombotic risk factors.