Situations in which a blood clot is more likely to form include:
- Being on long-term bed rest
- Crossing your legs for long periods when sitting, or sitting for long periods, such as in a plane or car
- During and after pregnancy
- Not having enough water in your body (dehydration)
- Taking birth control pills or estrogen hormones (especially in women who smoke)
- Long-term use of an intravenous catheter
Blood clots are also more likely in people with cancer, recent surgery or injury, obesity, and liver or kidney disease.
A buildup of cholesterol that narrows an artery may change or slow the flow of blood, making it easier for a blood clot or thrombus to form.
Conditions that are passed down through families (inherited) may make you more likely to form abnormal blood clots. Inherited conditions that affect clotting are:
A blood clot may block an artery or vein in the heart, affecting the: