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In vitro fertilization reported to increase blood clot risk

Robin Wulffson MD's picture
blood clot, thromboembolism, pregnancy, IFV, death

Currently, many couples with a fertility problem undergo in vitro fertilization (IVF) procedures that are not only costly but also associated with some health risks. A new study from researchers at the Karolinska Institute in Sweden has found that women who became pregnant through IVF are at increased risk for pulmonary embolisms and venous thromboembolisms, particularly during the first trimester (first three months) of pregnancy. They published their findings online on January 15 in the British Medical Journal.

A venous thromboembolism is a blood clot that forms in a vein, breaks loose, and travels to another area of the body where it causes a blockage. A pulmonary embolism is a blood clot that commonly forms in a calf vein and travels to the lungs where it causes blockage of blood flow to a portion of the lung. A thromboembolism can be fatal. The researchers set out to estimate the risk of pulmonary embolism and venous thromboembolism in pregnant women who underwent IVF. The study group comprised
23,498 Swedish women who had given birth after IVF between 1990 and 2008 and 116,960 individually matched women with natural pregnancies. The main outcome measures were the risk of pulmonary embolism and venous thromboembolism (identified by linkage to the Swedish national patient register) during the whole pregnancy and by trimester.

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The researchers found that venous thromboembolism occurred in 4.2/1000 women (99 women) after IVF compared with 2.5/1000 (291 women) in women with natural pregnancies. The hazard ratio for the women who underwent IVF was 1.77. (The hazard ratio is the increased risk of an occurrence; 1.0 represents no increased risk and 2.0 represents a two-fold risk.) The investigators found that the risk of venous thromboembolism was increased during the entire pregnancy and differed between the trimesters. The risk was particularly increased during the first trimester, at 1.5/1000 after IVF versus 0.3/1000. The proportion of women experiencing pulmonary embolism during the first trimester was 3.0/10 000 after IVF versus 0.4/10 000.

The authors concluded that IVF is associated with an increased risk of pulmonary embolism and venous thromboembolism during the first trimester. The risk of pulmonary embolism is low in absolute terms; however, because the condition is a leading cause of maternal mortality and clinical suspicion is critical for diagnosis, an awareness of this risk is important.

Take home message:
The primary culprit for the increased risk of thromboembolisms in pregnancy is believed to be the higher estrogen levels. An increased risk of thromboembolisms is a well-established side effect of normal pregnancies, occurring in one to two out of every 1,000 pregnancies. Certain factors increase the risk of a blood clot forming in any individual. Prolonged sitting, particularly with the legs crossed increases the risk as does smoking. Many individuals have a sedentary job. If so, it is important to get up and walk around periodically. Plane flights, bus trips, and long car trips also have a risk of thrombosis. Again, it is important to get up and stretch your legs periodically.

Reference: British Medical Journal