WASHINGTON (AP) -- New guidelines for the nation's obstetricians say it's time to pay more attention to the risk of blood clots in pregnant women getting C-sections, which account for nearly a third of U.S. births.

The recommendation is that doctors use compression devices, special inflating boots strapped around the legs, to lower the risk of a blood clot.

Hospitals already use these compression devices for other major operations.

The new recommendations promise to raise awareness of a silent threat, blood clots in veins that can masquerade as simple leg pain. They can be deadly if they travel up to the lungs.

A woman's risk of a DVT, or deep vein thrombosis, jumps during pregnancy and the six weeks afterward. That's partly because of slower blood flow from the weight gain, because mom is less active and because pregnancy temporarily changes blood to make it clot more easily.