If the fetus is found to be one week small in 4D ultrasound, there is no need to be overly nervous, one week small is normal, it can be improved by improving the mental state of pregnant women, nutritional intake, and can also be treated with medication under the guidance of the doctor. 1. Improve the mental state of pregnant women: no need to be overly nervous, maintain a good and calm state of mind, which is conducive to the growth and development of the fetus, appropriate exercise. 2. Adjust the nutritional intake of pregnant women: eat less fruits and vegetables with high water content, eat a reasonable diet, strengthen nutrition, drink more milk, and eat more high-protein food. 3. Medication: medication can also be used to enhance the blood circulation between the fetus and the mother, such as low molecular heparin, etc., which should only be used under the guidance of a doctor. If you find that your fetus is small in 4D for one week, you should pay attention to it, have regular maternity checkups, and carry out standardized treatment under the guidance of your doctor to ensure the normal development of your fetus.