Women who fall pregnant through in vitro fertilisation are at a higher risk of blood clots and artery blockages than women who get pregnant spontaneously, a new study has found.
The study, titled ‘Incidence of pulmonary and venous thromboembolism in pregnancies after in vitro fertilisation: cross sectional study’ and published in the journal BMJ, was conducted by researchers from the Karolinska Institute in Sweden, who examined data on the risk of pulmonary embolism (a sudden blockage in the lung artery) and venous thromboembolism (a blood clot in a vein) for 23,498 women who got pregnant through IVF and 116,960 women who fell pregnant naturally.
The average age of the women was 33 and they all gave birth between 1990 and 2008.
The risk of venous thromboembolism for IVF-pregnant women was 4.2 in 1000, but just 2.5 in 1000 for women who fell pregnant naturally. The risk was higher during the first trimester of pregnancy, the researchers found.
The risk of pulmonary embolism in women who fell pregnant through IVF was 3 in 10,000, compared to 0.4 in 10,000 for spontaneous pregnancies.
“In vitro fertilisation 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 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,” the researchers said.
The risk did not differ between the two groups of women before pregnancy and during the year after delivery and results did not change when the researchers adjusted for maternal age, BMI, smoking, country of birth and education.
Professor Robert Norman, director of the Robinson Institute at the University of Adelaide and a fertility specialist, said the results were not very surprising because the drugs used to stimulate ovulation could disturb coagulation and an operation was needed to harvest the eggs.
“Anyone who has an operation is at risk of clotting and deep vein thrombosis,” said Professor Norman, who was not involved in the research, adding that women whose ovaries were over stimulated by fertility treatments were particularly prone to getting blood clots.
“There are a number of women for whom clotting problems and fertility go together and sometimes we check women for clotting problems as part of our investigations.”
Women who fall pregnant through IVF are often more closely monitored by their doctors than women who fall pregnant naturally, so problems are also more likely to be identified, he said.
Women who fall pregnant through IVF should contact their doctor if they experience any symptoms of blood clots, such as pain in the legs, especially if there is a family history of clots, said Professor Norman.
IVFAustralia medical director Peter Illingworth said while the findings do indicate a need for vigilance on the risk of blood clots in IVF pregnancies, the actual effect is a very small one.
“The whole significance of this paper hangs on 4-5 extra cases of pulmonary embolism in the first trimester group out of 22,000 IVF pregnancies studied,” Associate Professor Illingworth said.
“Women considering IVF can be reassured that the risk of blood clotting in pregnancy, while serious if it happens, remains a very low risk indeed, regardless of whether the pregnancy is conceived with IVF or not.”
Professor Michael Davies, an epidemiologist at the University of Adelaide’s Lifecourse and Intergenerational Health Research Group, said women with a history of Preeclampsia) were also at increased risk of thromboembolism.
“Preeclampsia is overwhelmingly more common in first pregnancies and is also more common after IVF, particularly when using a donor embryo, which basically doubles the risk,” he said.
Further research was needed to find out why a higher risk of clots was linked to IVF, Professor Davies said.
“It could be, for example, that an aspect of treatment that’s altering the risk,” he said.
“Conversely, there may be a pre-existing medical condition such that women who are prone to thromboembolism may also be more likely to have fertility problems such as miscarriage or have early pregnancy loss, and therefore end up in an infertility clinic receiving treatment.”