The best time for four-dimensional color ultrasound examination during pregnancy Four-dimensional color ultrasound during pregnancy is a must-have examination for pregnant women during pregnancy, which can help the healthy growth of the baby and prenatal screening of pregnant women. But when is the best time to perform four-dimensional color Doppler ultrasound? This article will focus on four aspects: different stages of pregnancy, the purpose of examination, the physical condition of the pregnant woman and the doctor’s advice.