The phenomenon of swollen feet in the fourth month of pregnancy is caused by poor blood circulation. Because the fetus grows faster in the fourth month of pregnancy, the uterus will appear to be significantly enlarged, and it will compress the inferior vena cava, leading to obstruction of the return flow, which will lead to swollen feet and legs. During this period, you should pay attention to rest and avoid standing for a long time. You can elevate your lower limbs and put your feet flat to facilitate blood circulation and reduce the phenomenon of swollen feet. You should also pay attention to your diet, eat less salt, do not eat too greasy meat, and pay attention to blood pressure testing, because when blood pressure rises, it will also affect the filtration function of the kidneys, and edema will occur.