IVF increases risk of blood clots during pregnancy

A study published online by the British Medical Journal has shown that women who undergo in vitro fertilization (IVF) are at increased risk of pulmonary embolism (PE) and venous thromboembolism (VTE) during the first trimester.

Researchers from the Karolinska Institute in Sweden compared the risk of both PE and VTE in women undergoing IVF pregnancies (23,498) and those with natural pregnancies (116,960). Women were matched for age and time period (births between 1990 and 2008). The average age in both groups was 33 years.

The study found that the rate of VTE diagnosis in women who underwent IVF was 4.2 in 1000, compared with 2.5 in 1000 in those with natural pregnancies. Risk was increased during the first trimester (1.5 in the IVF group vs 0.3 in the non-IVF group). There was no difference in risk prior to pregnancy or during the year after delivery.

According to the report, results were not affected when adjustments were made for maternal age, calendar year of delivery, body mass index, parity, smoking, country of birth, family situation, or education.

The researchers concluded that there is an increased risk of blood clots-and importantly, an increased risk of artery blockage in pregnancy-after IVF. They recommended that doctors focus on identifying women at risk for PE and VTE, noting that absolute risks for PE were low, with 2 to 3 additional cases per 10,000 women undergoing IVF.