The large anomaly examination does not belong to level two or three in medicine. In clinical practice, the large anomaly examination refers to the four-dimensional color Doppler examination, which is neither a two-dimensional ultrasound nor a three-dimensional ultrasound examination.

During pregnancy, if there are no obvious abnormalities in the mother and the fetus, it is generally necessary to undergo a four-dimensional color Doppler examination, also known as the large anomaly examination, between 20-28 weeks of gestation to further understand whether the fetus has any malformations, and to understand the internal organs, body, limbs, and other parts of the fetus. It is also possible to check through the four-dimensional color Doppler examination, directly observing the movement of the fetus in the uterine cavity on the screen, and also observing the placenta, amniotic fluid, and other fetal accessories.

During pregnancy, the main contents of the anomaly examination include Down syndrome screening, NT, non-invasive DNA, amniocentesis, and so on. If there is a high risk of Down syndrome screening or abnormal NT test results, amniocentesis, non-invasive DNA testing, and other tests need to be performed, and a four-dimensional color Doppler anomaly examination is also required to further clarify the diagnosis and make a clear judgment on fetal malformations.