It is normal for the fetus to be one week smaller in ultrasound than in the last menstrual period.
During pregnancy, if the pregnant woman has a reasonable diet, proper exercise and all the prenatal examination results are normal, but the ultrasound examination of the fetus is one week small, then it may be the last menstrual period projection error, you can recheck the last menstrual period, the projected date of delivery.
However, if the pregnant woman suffers from malnutrition during pregnancy or has a combination of gestational diseases such as hypertension, pre-eclampsia, gestational diabetes, etc., if the fetus is found to be one week small, the pregnant woman should be allowed to have a reasonable diet, actively treat the relevant diseases, and monitor the growth trend of the fetus in a timely manner.
The fact that the fetus is found to be one week small in the prenatal period usually has no effect, but it should be strictly on time to carry out obstetric examinations.