Mild swelling of the feet of a pregnant woman at 18 weeks of pregnancy is usually normal. When a pregnant woman is pregnant, the human body, in order to ensure the normal development of the fetus, will undergo corresponding structural as well as functional changes, such as an increase in renal blood flow and a corresponding increase in glomerular filtration rate, so that the patient’s toxin levels, such as blood creatinine and urea nitrogen, are at a low level compared to normal. When a pregnant woman is pregnant from the 3rd month, i.e. 12 weeks, the systemic blood volume increases significantly, which, together with the increased levels of progesterone and estrogen in the body, can lead to varying degrees of edema. If the edema is mild, i.e., it appears on the face and limbs, it is usually not a big problem. However, if the edema occurs above the lower legs bilaterally, i.e. above the knee joints, it is an abnormal phenomenon. At this time, it is necessary to test the urine routine of the pregnant woman, observe whether there is a situation of urinary protein, and observe whether the patient’s blood pressure is hypertensive, and if there is the occurrence of the above situations, it is necessary to closely observe the pregnant woman to prevent the emergence of hypertensive syndrome of pregnancy.