An increase in the tendency of the blood to clot, as in 'thrombosis'. In primitive, evolutionary times, a survival advantage for women giving birth, when loss of blood would on average be less, but exacting a price in terms of increased risk of stroke or venous thrombosis. The thrombophilias are implicated in disturbances of pregnancy, including recurrent miscarriage and stillbirth.

A polymorphism for blood clotting factor "five" that makes coagulation occur more readily, therefore causing thrombophilia. Pronounced "Layden".

A polymorphism affecting the metabolism of folic acid with a number of possible consequences avoidable by increasing dietary supplements to mega-doses (5 mg to 10 mg per day), including promotion of blood coagulation, or thrombophilia, abnormalities of the fetus (birth defects, especially neural tube defects such as spina bifida and anencephaly), recurrent miscarriage, an increased chance of heart disease and coronary thrombosis, and in men, possibly contributes to oligospermia and infertility.

A polymorphism for the blood clotting factor prothrombin that makes coagulation occur more readily, therefore causing thrombophilia.