In many cases DVT develops for no known reasons. However, there are some risk factors that mean a person is more likely to develop DVT, including:
Inactivity – Being unable to move for long periods of time can affect the blood flow, leading to it slowing down. While, in most cases this isn’t a cause for concern, it does increase the risk of a blood clot forming.
Being in hospital – As DVT is more likely to occur if you’re inactive or unwell, being in hospital can also increase the risk. If you have had an operation that lasted more than 90 minutes, are having an operation for an inflammatory or abdominal condition, or are confined to bed, you’re also at a greater risk. However, the risk of DVT in hospital should be assessed and preventive measures taken.
Blood vessel damage – Trauma, such as broken bones or severe muscle damage, can affect the blood vessels. In some cases it may lead to vessels becoming blocked or narrowing, which may lead to a blood clot forming. Some conditions and medication can also lead to blood vessel damage.
Medical and genetic conditions – There are some medications and genetic conditions that can increase the risk of DVT as they mean your blood clots easier than normal. These include chemotherapy, heart disease, rheumatoid arthritis, and lung disease.
Pregnancy – The blood naturally clots more easily when a person is pregnant. Around one in 100,000 pregnant women will be affected by DVT and pulmonary embolism, a complication of the condition. Although rare, being pregnant means you’re up to 10 times more likely to develop the condition.
Contraceptive pill and HRT – Both the contraceptive pill and hormone replacement therapy have been linked to DVT due to them both containing oestrogen. If you take either of the medications your risk should be monitored.