The fetal nasal bone will grow out at the latest around 14 weeks. The fetal nasal bone usually forms at 11-14 weeks and can be viewed during the ultrasound examination at 11-14 weeks of pregnancy. However, occasionally, due to the fetal position, the facial development may not be seen temporarily and can be reviewed after 1 week. However, if the nasal bone remains undetectable beyond 16 weeks, you need to consider whether it is a developmental abnormality. It can be reviewed periodically to observe the fetal systems such as cardiovascular, gastrointestinal and renal development for abnormalities and chromosomal abnormalities, and if no abnormality is seen, we can wait until the fetus is delivered. In general, nasal bone loss indicates chromosomal abnormalities in the fetus, mostly Down syndrome, also known as trisomy 21, which can lead to developmental delay, mental retardation, combined with organ malformation and functional disorders. After nasal bone loss is confirmed, non-invasive DNA test or amniocentesis is performed to diagnose the condition and decide whether to terminate the pregnancy according to medical advice.