Up to one in 12 women unknowingly carry a genetic mutation that increases their risk of having blood clots when taking the Pill.
Everyone inherits two copies of a gene called factor V (F5) from their parents, which is vital for blood to clot properly in the event of an injury.
However, eight per cent of people have a mutated version that triggers a disorder called Factor V Leiden. While it causes no symptoms, it raises their risk of