It is not too late to have a 4D ultrasound at 26 weeks of pregnancy. But in fact, 4D ultrasound can be performed at 22 weeks, and no later than 28 weeks. After 20 weeks of pregnancy, the fetal limbs and major organs are fully developed. Between 22 and 26 weeks of pregnancy, the fetal organs are more fully developed, and there is more amniotic fluid and enough space to move around, which is more convenient for examination. The fetal eyes, lips and nostrils are slowly formed at 26 weeks of pregnancy, and the fetal limbs and internal organs are basically well developed. 4D ultrasound can observe the growth and development of the fetus in utero in multiple directions and angles, and can perform three-dimensional imaging of the fetal head and face, which can clearly show the state of the fetal eyes, nose, mouth and jaw, and can assist doctors in directly diagnosing fetal congenital malformations, such as cleft lip, spina bifida, brain It can assist doctors in directly diagnosing congenital malformations such as cleft lip, spina bifida, brain, kidney, heart and bone dysplasia. It is necessary to make an appointment in advance for the 4D ultrasound examination. The day before the examination, it is necessary to pay attention to sufficient rest, and on the day of the examination, pay attention to eating before going for the examination, so as to avoid that the fetal activity in the uterus will be reduced in the hungry state, which will affect the examination results. In addition, pay attention to do the examination after emptying the bladder to avoid the ultrasound examination results being affected by a full bladder.