When do you do 4D color?

Nt examination is generally to choose pregnancy to about 11 weeks when nt examination, and then pregnant to 22 weeks when you can do four-dimensional color Doppler ultrasound, within 24 weeks to do four-dimensional color Doppler ultrasound is relatively good, and then do Down's screening, the best time is pregnant, 16~18 weeks to do Down's screening is the most appropriate. Do Down's screening can generally clearly judge whether the fetus has Down's syndrome, so many examinations during pregnancy are very necessary to do, first is nt examination, followed by four-dimensional color Doppler ultrasound, and then Down's syndrome.