 if you think dangerous blood clots can't happen to you think again up to 900 000 men women and children are affected by blood clots each year and about 100 000 die from them blood clots don't discriminate you or a loved one could be at risk right now the good news is blood clots can be prevented knowing the risks and symptoms are key major risks for blood clots include a family or personal history of blood clots a recent hospitalization or surgery pregnancy and cancer and its treatments