Pregnant women can lower blood clot risk during flights

Pregnant air travellers face a higher risk of blood clots, but they can reduce their risks by walking airplane aisles, drinking water and doing calf exercises, according to a new review.

For women with additional risk, doctors may recommend compression stockings and injectable blood thinners while traveling, the authors write in the Journal of Travel Medicine.

"Both pregnancy and air travel are risk factors for venous thromboembolism, or a blood clot in the legs or lungs," said senior author Dr. Leslie Skeith of the University of Calgary, a member of the CanVECTOR Canadian thrombosis research network.

Blood clots affect about one to two per 1,000 non-pregnant people each year and are the third leading cause of vascular death after heart attacks and strokes, the authors note. With more than two billion passengers flying each year, about 150,000 cases of travel-related blood clots are diagnosed annually.

Long-distance flights tend to increase the risk by three-fold, yet travel-related studies either don't include pregnant women or only include a small number and don't directly investigate how pregnancy increases the risk.

"There is very little evidence to guide what pregnant and postpartum women should do to prevent blood clots while travelling," Skeith told Reuters Health by email.

Skeith and her colleagues review the many factors that play into an individual's risk for a blood clot, including height, weight, recent surgery, pregnancy, use of oral contraceptives, hormone replacement therapy and a family history of clots or diseases that promote clotting.

Why pregnancy heightens clot risk

With pregnancy in particular, they write, the risk is higher because of physiological changes, such as slower blood flow and blood vessel dilation. Pelvic blood vessels may also be compressed as the uterus grows. Starting in early pregnancy, the body starts to become hypercoagulable, or more likely to form blood clots. These risks remain higher until about 12 weeks after giving birth.

Although the average pregnant or postpartum air traveler faces an increased risk of clots, the absolute risk estimate is low at less than 1 per cent, the study found.

Pregnant women with other risk factors, such as inherited blood problems, obesity and recent surgery, may face a higher blood clot risk, however. Although the risk depends on individual factors, women with a history of blood clots tend to have a four per cent higher risk while pregnant, and those with hormonal-associated blood clots tend to have a six per cent higher risk while pregnant.

For most women with a history of blood clots, the risk during air travel still remains low at just over one per cent. At the same time, pregnant women who face these higher risks should consider using more extensive blood clot prevention measures while travelling, such as the injectable blood thinner low-molecular-weight heparin (LMWH).

Aspirin trial begins

"It is known that LMWH prophylaxis lowers the risk of recurrent thrombosis in women with previous venous thromboembolism," said Dr. Ida Martinelli of the University of Milan, who wasn't involved in the study.

However, some studies show that certain blood conditions and blood thinners can lead to complications during delivery, so it's best to consult a doctor for individual recommendations.

Skeith and colleagues are now studying whether aspirin can prevent blood clots in postpartum women with risk factors for clots. The pilot randomized trial, called PARTUM, is expected to start in 2020.

"We desperately need more research to better prevent blood clots in pregnant and postpartum women," Skeith said. "We recommend talking to your doctor about different options."