IVF increases risk of blood clots during pregnancy, say scientists

Women who conceive using IVF are at an elevated risk of lethal blood clots during pregnancy, a study has found. Researchers looked at the medical records of 20,000 women who conceived using IVF and compared their findings to 100,000 women who conceived naturally.

'Our finding is... important to health professionals dealing with women who are recently pregnant after [IVF]', writes Professor Peter Henriksson, lead author of the study at the Karolinksa Institute, Sweden.

The rate of blood clots in veins, called venous thromboembolisms, increased from approximately 25 per 10,000 women with natural pregnancies to 42 per 10,000 women with IVF pregnancies. A small increase in the rate of blood clots in arteries supplying the lungs, called pulmonary embolisms, was also found in IVF pregnancies, increasing from six cases to eight per 10,000 women. Although the increased rate of blood clots was significant, the absolute risk remained low.

'The risk of pulmonary embolism is low in absolute terms but because the condition is a leading cause of maternal mortality... an awareness of this risk is important', writes Professor Henriksson.

The increased risk was at its highest during the first three months of pregnancy, after which there was no difference between the women who conceived naturally or using IVF. In order to rule out confounding factors that may have affected the results of the study, the researchers age-matched the IVF mothers with those who had conceived naturally. They also took into account whether the women were smokers, had multiple births and their body mass index (a read-out of human body fat).

The increased occurrence of life-threatening blood clots in IVF pregnancies was suggested to be due to the IVF technique itself, although further research is required to determine whether this is indeed the case.

Professor Henriksson told the Mail Online: 'During the IVF procedure hormonal drugs are given to stimulate the egg follicles to grow more eggs. This increases oestrogen levels in the body between ten and 100-fold and is likely to impact on the coagulation of the blood and increase blood clot formation'.

The study, published in the British Medical Journal, calls for increased vigilance for pulmonary embolism and to consider the use of anti blood clotting drugs during pregnancy for women planning to undergo IVF.