From MedlinePlus Genetics
Prothrombin thrombophilia is a disorder that increases the risk of developing blood clots. Thrombophilia is the term used to describe an increased tendency to form blood clots. After an injury, clots protect the body by sealing off damaged blood vessels and preventing further blood loss. People with thrombophilia can develop clots when they are not needed. These clots can block normal blood flow and cause harm.

People who have prothrombin thrombophilia have a higher-than-average risk of developing a type of clot called a deep vein thrombosis, which typically occurs in the blood vessels of the arms or legs. People with prothrombin thrombophilia also have an increased risk of developing a pulmonary embolism, which is a clot that travels through the bloodstream and lodges in the lungs.

Research suggests that pregnancy loss may be somewhat more likely in people with prothrombin thrombophilia than in those who do not have the condition. Some researchers have suggested that prothrombin thrombophilia may also increase the risk of other complications during pregnancy, though this remains controversial.

While many people with prothrombin thrombophilia will never have clotting issues, several factors increase a person's risk of blood clots. Some risk factors that contribute to the development of harmful blood clots include surgery, injury or trauma, air travel, obesity, and a family history of blood clots. Additional risk factors include pregnancy, using contraceptives such as birth control pills or patches that contain estrogen, and receiving post-menopausal hormone replacement therapy. The combination of prothrombin thrombophilia and other clotting disorders may also increase a person's risk.  https://medlineplus.gov/genetics/condition/prothrombin-thrombophilia