A fetus that is one week small is a fetus that is at an alarming size and may be caused by a miscalculation of the due date, poor maternal nutrition, or restricted fetal growth. This situation needs to be concerned, pregnant women should be in the hospital obstetrics to identify the causes and take appropriate measures. Common causes and treatment 1, the prenatal period calculation error: in the case of irregular menstrual cycle of women, the calculation of the prenatal period may be inaccurate, which may also lead to the fetus compared to the delivery date of one week, the doctor needs to recalculate the prenatal period according to the ultrasound, after checking the pregnancy week, if the size of the fetus is in line with the pregnancy week, pregnant women do not need to take other treatment measures; 2, malnutrition of pregnant women: due to dietary habits or pregnancy Reactions often result in loss of appetite during pregnancy, which in turn leads to malnutrition of the fetus and a week on the small side. Pregnant women can use diet adjustment after the end of pregnancy reaction, eat more vitamin and protein-rich food to supplement nutrition, and also use drugs to supplement scarce elements in the body under the guidance of doctors, such as iron supplements, calcium supplements, etc.; 3, fetal growth restriction: if combined with gestational hypertension disease, pre-eclampsia, gestational diabetes, etc. may affect the function of the placenta, thus causing fetal growth and development is small. In this case, the relevant lesions should be treated actively in order to restore the fetal growth to normal. After confirming her pregnancy, women should strictly regulate their dietary habits, eat more foods that are beneficial to the fetal development, and go to the obstetrics department of the hospital for regular physical checkups to confirm their physical condition and fetal development.