IVF blood clot risk

In vitro fertilisation may raise the risk of blood clots and blocked arteries – although the risk is small, researchers warn today.

The rate of in vitro fertilisation (IVF) is increasing around the world. Although the risk of pulmonary embolism (blockage of the main artery of the lung) and venous thromboembolism (blood clots) is known to rise during normal pregnancy, it may be more common after IVF.

A team led by Professor Peter Henriksson of the Karolinska Institute, Sweden, set out to estimate the exact risk using figures on 23,498 pregnancies due to IVF and 116,960 natural pregnancies.

Venous thromboembolism affected 4.2 in 1,000 women after IVF compared with 2.5 in 1,000 in women with natural pregnancies. This equates to a 77 per cent raised risk. While risk was increased during the whole pregnancy, it was particularly increased in the first trimester. Pulmonary embolism was also significantly raised during the first trimester with IVF.

The link was not influenced by maternal age, body mass index, number of previous children, smoking, country of birth, family situation or education.

In British Medical Journal, the authors conclude: "The risk of pulmonary embolism is low in absolute terms, but because the condition is a leading cause of maternal mortality and clinical suspicion is critical for diagnosis, an awareness of this risk is important.

"Doctors should be aware of these increased risks because the symptoms of pulmonary embolism can be insidious and the condition is potentially fatal," they write. "Efforts should focus on the identification of women at risk of thromboembolism, with prophylactic anticoagulation considered in women planning to undergo in vitro fertilisation."

Henriksson, P.et al. Incidence of pulmonary and venous thromboembolism in pregnancies after in vitro fertilisation: cross sectional study. BMJ January 16 2013 doi: 10.1136/bmj.e8632