Pregnancy and Hormone Therapy

Changes in Hormone Balance Brings Increased Risk of Clotting

The most common cause of maternal death during pregnancy is a blood clot, with an incidence of one to five per 1,000 pregnancies, including the period immediately following childbirth. In women with a previous history of deep vein thrombosis, the risk of additional deep vein thrombosis with pregnancy is 12-35% and increases to 75% in women with inherited clotting disorders.

Causes of pregnancy-related blood clots include:

• Decreased levels of natural anticoagulants such as antithrombin, or total and free protein S

• Increased levels of clotting proteins such as FVIII, von Willebrand factor, and fibrinogen

• Decreased rate of blood flow, increasing the risk of blood pooling, especially in the legs

HORMONE THERAPY

Estrogens and oral contraceptives mimic hormone levels found in the pregnant state, leading to clotting protein changes. The use of hormone therapy may, therefore, lead to an increased risk of blood clots, especially in women with clotting disorders, such as factor V Leiden.