Final answer:
A pregnant woman is most at risk for DVT during the third trimester due to increased pressure on pelvic blood vessels and other circulatory changes.
Step-by-step explanation:
A pregnant woman is most at risk for a DVT (Deep Vein Thrombosis) during the third trimester of pregnancy.
During this period, the uterus expands rapidly, and as the fetus grows larger, there's increased pressure on the pelvic blood vessels which hampers venous return from the legs, potentially leading to the formation of blood clots.
Factors such as increased blood volume and moderate rises in pulse and blood pressure during pregnancy further contribute to the risk, along with potential pooling of blood from prolonged sitting, as might occur during air travel.