NT normal Down’s syndrome is a critical risk, generally do not have to worry too much, but can not rule out the possibility of fetal Down’s syndrome, should be further examination to determine whether the fetus has chromosomal abnormalities. NT normal down screening critical risk may be and early pregnancy birth control, take birth control drugs is related, if in early pregnancy to take birth control drugs, may cause human chorionic gonadotropin value is high, resulting in rapid heartbeat, panic chest tightness, dyspnea and other symptoms, the test results will show a critical risk or high risk situation. Down syndrome can be caused by genetic factors, an increase in the number of chromosomes, chromosomal abnormalities or exposure to undesirable factors such as too high a dose of radiation, drugs with too high a teratogenicity rate or a polluted workplace. If the patient has a NT normal Down’s test but critical risk, an amniocentesis can be done under the supervision of the doctor to determine whether the fetus has the possibility of Down’s syndrome.