The AC in fetal ultrasound results refers to the abdominal circumference, which is one of the indicators to estimate the size of the fetus and to check the expected date of delivery. The fetal abdominal circumference varies according to the week of gestation. The fetal abdominal circumference is about 20.5 cm at 24 weeks of gestation and 32.5 cm at 36 weeks of gestation. if the fetal abdominal circumference is large, it means the fetus is likely to be large, while if the fetal abdominal circumference is small, it means the fetus is likely to be relatively thin and small. However, the abdominal circumference standard is only a general reference value, because the individual itself varies greatly, so the actual situation should be considered in conjunction with individual data factors such as the height and weight of the pregnant woman before pregnancy. The abdominal circumference can also be used to calculate and check the expected date of delivery, the doctor can estimate the gestational age and project the expected date of delivery by measuring the inter-parietal diameter of the fetal head, abdominal circumference, head and hip length and femur length during the ultrasound, this method is mostly used as a diagnostic application for the doctor’s ultrasound examination.