The first reason is that the examination time is too early, the fetal nasal bone is not fully developed, many pregnant women in the first eleven weeks of pregnancy to do obstetrics, this time the ultrasound may not show the nasal bone or show incomplete, which is very easy to cause the psychological burden of pregnant women. In fact, there is no need to worry too much about this, it is recommended that the pregnant woman wait for 12 weeks and then go to do a retest. In the second case, if the pregnant woman can’t see the nasal bone or the nasal bone doesn’t show up even after several ultrasound examinations after 12 weeks of pregnancy, then this situation suggests that Down’s syndrome is possible. If this phenomenon occurs, it is recommended that the pregnant woman do further tests as soon as possible, and the exact results of the tests need to be carefully selected and considered by the pregnant woman, her family, and her doctor.