Smaller fetus may be caused by irregular menstruation, malnutrition, abnormal fetal development, etc. Depending on the situation, regular monitoring, nutritional supplementation and termination of pregnancy can be taken to remedy the situation. 1. Irregular menstruation: Irregular menstruation of pregnant women can lead to the actual number of weeks of the fetus is small, the fetus is small, the measurement value is within two times the standard deviation of the corresponding gestational weeks, it is a normal physiological phenomenon, do not need to take remedial measures, regular monitoring and observation can be. 2. Malnutrition: After pregnancy, pregnant women vomiting reaction is more serious or excessive picky eating, may lead to the lack of nutrients in the body, the phenomenon of poor fetal development and small. This can be remedied by dietary adjustments, eating more nutritious food, such as milk, beef, eggs, fish and shrimp and other foods. 3. Fetal development abnormalities: after pregnancy, if the fetus has chromosomal abnormalities, it will affect its normal growth and development, which may lead to slow fetal growth and development, the phenomenon of small fetus, it is recommended to go to the hospital through ultrasound, non-invasive DNA, amniocentesis and other tests to determine if the diagnosis of more serious malformations should be followed by the doctor’s advice to terminate the pregnancy in a timely manner. There are many possible reasons for small-sized fetus, which should be handled and treated according to the specific reasons.