The risk of blood clots after surgery is 70 times that of patients who haven't undergone surgery, according to a 2009 study reported by WebMD. Risks are particularly high during the first six weeks after surgery and remain significant for up to three months post-surgery.
Even minor outpatient surgery, such as a biopsy, increases the risk of a blood clot tenfold, according to WebMD. In the reported study, one out of every 140 women who had surgery was readmitted for blood clots within three months. The riskiest operations are hip replacements, knee replacements and other major orthopedic procedures, followed by cancer surgery. The lack of movement that follows orthopedic surgery may be to blame for the higher incidence of blood clots.