At 24 weeks of pregnancy, the normal measurement of the fetal nasal bone is 4.5 mm or more. If the measurement of the nasal bone is less than 4.5 millimeters it is not normal and it is considered that there may be developmental abnormalities. The measurement process requires a precise measurement method to avoid errors due to inaccurate measurements. Nasal bone measurements are performed during the 11th to 14th week of pregnancy. The ultrasound measurement of the nasal bone, combined with the NT value, is used to estimate whether the fetus is at risk for Down syndrome, and is a soft indicator for chromosomal abnormalities. This test avoids the complications associated with invasive tests, is quick, convenient, reproducible, and inexpensive, and allows for the detection of abnormalities at an early stage and early prenatal diagnosis. The nasal bone of the fetus can also be measured in the middle and late stages of pregnancy, and the results need to be analyzed in conjunction with other indicators in order to clarify their specific significance.