Increased Blood Clot Risk on the Pill

More bad press for the pill, this time the focus is on the combined oral contraceptives - the kind containing both the hormones oestrogens and progestin. If the woman taking these pills has a common vein malfunction (experienced by a quarter of the population), her risk of blot clots is increased significantly.

'Up to 25% of the healthy population has a narrowing, known as stenosis, in the left common iliac vein (one of two major veins deep in the pelvis that return blood from the lower body to the heart), according to Dr Lawrence Hofmann and his colleagues at Stanford University School of Medicine.

In their study, published in the American Journal of Obstetrics and Gynaecology, having a "left common iliac vein stenosis" and taking so-called combined oral contraceptives - the kind containing both the hormones oestrogens and progestin - multiplied a woman's risk of deep vein thrombosis nearly 18 times compared to women with neither risk factor.

Sometimes known as "economy class syndrome", a deep vein thrombosis is a blood clot - often formed in veins of the lower legs – which is potentially dangerous because it can travel to the heart and lungs and cause serious harm.

Some 12 million women in the US use the "combined" form of birth control pill, which is already known to increase a woman's risk of blood clots.

In general, the researchers note, among every 10,000 young women who are not taking oral contraceptives, about one to three will have a deep vein thrombosis every year. For young women who've been taking the Pill for a year, that risk goes up six-fold.'

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