It makes no difference whether the 4D ultrasound is done in the morning or in the afternoon, so there is no time period that is better. The 4D ultrasound is a very important test during pregnancy, through which you can find out how the fetus is growing and developing. The 4D ultrasound needs to be done twice during pregnancy. The first 4D ultrasound is done between 22 and 26 weeks of pregnancy and the second 4D ultrasound is usually done around 30 to 32 weeks of pregnancy. The 4D ultrasound can see the development of the fetus’s face as well as its limbs, and help determine whether there are congenital heart defects, absence of internal organs, defects in the abdominal wall, congenital spina bifida, anencephaly, cleft lip and palate, and so on. Four-dimensional ultrasound usually needs to be booked in advance at the hospital, and there is usually no radiation, no need for fasting and holding urine. It is recommended to make reasonable arrangements in accordance with the weeks of your pregnancy, and you can consult a professional physician for advice on specific matters.