HC in the ultrasound examination of pregnant women represents the head circumference of the fetus. The HC in the ultrasound represents the head circumference of the fetus at that stage of development, which is an important indicator of the fetus’ physical development and can be used with other indicators to calculate the height and weight of the fetus. There is a normal range of head circumference at each stage of fetal development. If the head circumference is within the normal range at the time of examination, or if it does not vary much, most of them are not abnormal. If the size of the fetus’ head circumference varies too much from the normal value at this stage, it is considered to be due to pathology or maternal malnutrition and the cause needs to be checked and treatment chosen.