What's the difference between NT and 4D?

NT examination and four-dimensional examination are different. NT examination is carried out from 11 weeks to 13+6 weeks of pregnancy. This examination is to detect the thickness of the transparent layer behind the neck of the fetus. If it exceeds 3mm, it is abnormal and further examination is needed. Four-dimensional examination is also the examination of fetal large row abnormality. The time of examination is between 24-27 weeks of pregnancy. At this time, it is mainly to see if the fetus has developmental abnormalities. Therefore, these two kinds of examination times are different. The nt thickening may be caused by Down's syndrome, which means that it is caused by abnormal chromosome development, or it may be caused by fetal heart malformations. If the examination is large, it is to examine various parts of the body, mainly to see if there are fetal malformations.