DVT (Deep Vein Thrombosis)

A deep vein thrombosis is a blood clot in a deep vein, usually in the calf or thigh. It matters because part of the clot can break off and travel to the lungs, a pulmonary embolism, which can be life-threatening. Estrogen raises the risk.

Where you'll meet it

In the risks section of any conversation about estrogen, on surgical consent forms, and in the question of whether to pause hormones before an operation.

Why estrogen matters

Estrogen makes the blood a little more prone to clotting. How much depends on the type and route. The old synthetic estrogen, ethinylestradiol, carried a clearly higher risk and is no longer recommended for trans women. Oral estradiol passes through the liver first, which raises clotting factors more than estradiol through the skin (transdermal) or by injection. For someone with other risk factors, that is often why a prescriber suggests patches or gel.

What adds to the risk

Smoking is the big one. Others are age, being inactive for long periods, long-haul flights, a personal or family history of clots, some inherited clotting conditions, and surgery. Several of those tend to stack up at once when people travel abroad for an operation, which is why surgeons ask about hormones well before the date.

Signs to know

Pain, swelling, warmth or redness in one leg, usually the calf. Sudden breathlessness, chest pain that is worse on breathing in, or coughing up blood are signs of a clot in the lung, and need emergency care straight away. Hormones and surgery covers the pre-operative question.

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