The 4D ultrasound is the most important and comprehensive screening test for prenatal anomalies during the 18-24 weeks of pregnancy. The 4D ultrasound also includes more and more comprehensive items than other ultrasounds during pregnancy. The 4D ultrasound report contains: 1. The number of fetuses. 2. 2, Fetal heartbeat, the fetal heart rate should be 120 to 160 beats per minute during this period. 3, Biological measurements (biparietal diameter, transverse cerebellar diameter, length of the humerus and femur, abdominal circumference, and other data measured in standard sections and the week of gestation and weight assessed by ultrasound on this basis) 4, Examination of fetal anatomy (fetal head to be observed cranial bones and their intracranial structures, fetal face, neck, chest, heart diaphragm, abdomen, spine, limbs). 5, placenta (requires observation of the location of the placenta, maturity, the relationship between the lower edge of the placenta and the inner opening of the cervix, etc.). 6, Umbilical cord (requires observation of the number of umbilical cord vessels, the placental entrance to the umbilical cord, and the entrance to the fetal abdominal wall, etc.). 7, Amniotic fluid volume. 8, Maternal uterus and double adnexa. If the 4D ultrasound examination of the fetus and the mother there are abnormalities, will be in the final ultrasound diagnosis or ultrasound prompted by the place to show. Normal fetus will usually suggest the gestational week and weight of the fetus. Although 4D ultrasound is the most comprehensive screening for malformations during the fetal period, there are limitations to 4D ultrasound and not all types of malformations can be screened for.