How is pregnancy associated with an increased risk of pulmonary embolism?

Estrogens: The increased circulating Estrogens have a pro-thrombotic effect, making clotting more likely. To a lesser degree, the pregnant uterus may constrict the vena cava, which can lead to dvt, but this effect is not as powerful as the hormones.

Blood clots: The main reason for the increased risk during pregnancy is the change in blood clotting. Pregnancy hormones are believed to change how the blood the clots. Reduced venous blood flow from the legs may also predispose to a blood clot that may break off and travel to the lungs i.e. Pulmonary embolism.

PE: The pressure of the fetus on the lower extremity veins can help blood clots form in the leg and pelvic veins if there is a clotting diathesis. If a clot forms the pulmonary embolism can happen.

Deep vein thrombus: Weight gain edema stasis in veins obstruction of vena cava and iliac veins by weight and pressure of pregnant uterus coagulopathies of pregnancy less mobility of some folks-sedentary clots form, extend and embolize to the big filter- the lungs.