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Hormones linked to deep vein thrombosis in women

Whether you are pregnant, are considering birth control or want to take hormone replacement therapy, it is important to be aware that changes in hormone levels can put women at greater risk of developing deep vein thrombosis.

Deep vein thrombosis (DVT) refers to a blood clot in a vein, usually in a larger vein deep in the leg, especially in the calf. Leg movements help blood to flow through the veins by squeezing them, so long periods of immobility, such as when travelling or during surgery, can slow down blood flow and allow it to clot.

The blood clot can block the flow of blood through the vein, either partially or completely. If it breaks off, it can travel to the lung, causing a serious complication known as pulmonary embolism, in which there may be a sudden cough producing blood, chest pain or tightness, burning or aching in the chest, sudden shortness of breath or collapse. Pulmonary embolism can be fatal, and anyone with these symptoms should call for an ambulance or go to the A&E department in the nearest hospital.

Blood clots occur in both men and women, however, there are certain hormonal changes that increase the risk of DVT only in women:



Although only one to two in 1,000 pregnant women will develop DVT during pregnancy or within 6 weeks of giving birth, it's a greater risk than women who are not pregnant. Blood flows more slowly in pregnant women, which increases their risk of DVT, as does the pressure the growing womb ( uterus) can put on their veins. Blood also clots more easily in pregnant women to help the placenta and prevent too much blood loss during childbirth.

Birth control

Contraception that includes the hormone oestrogen, such as the combined pill, can slightly increase the chances of blood clotting more readily. For most women, this isn't a problem but if you are significantly overweight, smoke cigarettes, are over 35 years old, there is a family history of DVT or you have high blood pressure or high cholesterol levels, you may be advised to consider oestrogen-free methods such as a progesterone-only pill, implant or IUD.

Hormone replacement therapy (HRT)

Menopausal women who take HRT that contains oestrogen have a slightly higher risk of DVT of about 2 in every 1,000 women between 50 and 59 years old. The benefits could outweigh the risks, so discuss with your GP what options might be best for you.

DVT precautions

Even if you are pregnant or using birth control or taking HRT, you can help prevent blood clots by taking some precautions. If you plan to travel a long distance by plane, train or car, or for some reason you need to get plenty of bed rest, ensure that you:

  • Drink lots of fluids to keep hydrated (limit or avoid caffeinated and alcoholic drinks)
  • Wear loose-fitting clothes that won't constrict your movement
  • Try to walk about or at least stretch and move your legs every hour
  • Consider wearing a pair of compression stockings, available in the travel section of supermarkets and pharmacies to help keep blood flowing through your veins, but first check with your GP - people with certain medical conditions, such as diabetes, should not use them.

If you are pregnant and develop a blood clot, had a previous clot, or have a blood clotting disorder, or you need to have bed rest or a caesarean section, your doctor may prescribe you an anticoagulant medicine such as heparin, which is safe to take during pregnancy. If you are in hospital, such as after a caesarean section, you may need to wear special elastic stockings or inflatable boots, which squeeze your muscles to keep blood flowing.

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