(HealthDay News) – Pregnant women have an increased risk of venous thromboembolism and pulmonary embolism after in vitro fertilization (IVF), especially during the first trimester, according to a study published online Jan. 15 in BMJ.

Peter Henriksson, MD, of the Karolinska Institutet in Stockholm, and colleagues conducted a cross-sectional study to estimate the risk of pulmonary embolism and venous thromboembolism during the pregnancy and in each trimester after IVF. The population comprised 23,498 women who had given birth following IVF between 1990 and 2008, who were matched with 116,960 women with natural pregnancies.

The researchers observed a significantly increased risk of venous thromboembolism after IVF vs. natural pregnancies (4.2 vs. 2.5 per 1,000 women; hazard ratio, 1.77). The increased risk was seen during the whole pregnancy and varied between the trimesters, with a particular increase noted during the first trimester (1.5 vs. 0.3 per 1,000 women; hazard ratio, 4.22). During the first trimester, significantly more women experienced pulmonary embolism after IVF vs. natural pregnancy (3 vs. 0.4 per 10,000 women; hazard ratio, 6.97).

“Our results show an increased risk of thromboembolism and, importantly, pulmonary embolism in pregnant women after in vitro fertilization,” the authors write. “Doctors should be aware of these increased risks because the symptoms of pulmonary embolism can be insidious and the condition is potentially fatal.”

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