Fetal venous catheter a-wave reversal on NT is serious and requires further investigation to clarify the abnormality and early treatment. Fetal venous catheter a-wave reversal suggests the presence of severe intrauterine distress, which may be related to the presence of fetal cardiac malformations and chromosomal abnormalities. Pregnant women can undergo Down screening or non-invasive DNA screening for fetal chromosomal aneuploidy abnormalities, amniocentesis, color ultrasound prenatal diagnosis if necessary, to clarify the cause and timely intervention and treatment. NT predicts the intrauterine oxygen supply of the fetus through the changes of blood flow. Initial hypoxia is found to be the disappearance of the diastolic flow of the umbilical vein of the fetus, followed by the appearance of the reversal of the diastolic flow of the umbilical artery, and lastly, the reversal of the a-wave of the fetal venous catheter, which suggests that there is a serious intrauterine distress, and it is predicted that the fetus is very likely to die in the short term, and it should be taken to the hospital as soon as possible to get medical treatment.