Why do some pregnant women have edema?

Women during pregnancy, some people appear edema phenomenon, which can be divided into physiological edema and pathological edema, physiological edema is due to the third trimester of pregnancy women, uterus gradually enlarged, oppression of lower limb veins, resulting in reflux blocked edema symptoms, generally after rest can be relieved. Pathological edema is caused by pregnancy hypertension, pregnancy complicated with kidney disease.