Ultrasound is done 4-5 times during pregnancy. The first ultrasound is usually done at 6-7 weeks of pregnancy to observe the location of the gestational sac, the size of the sac and the development of the fetal buds. The second ultrasound is at around 13 weeks of pregnancy, when the fetus has already taken on a human shape, and the skull, limbs and spine can be seen, and it is necessary to observe whether there are any major malformations, such as anencephaly, spina bifida, and also to measure NT to rule out Down’s syndrome. The third ultrasound is done at 24-28 weeks of pregnancy, when the development of all parts of the fetus’s body has basically taken shape. Ultrasound should be done to systematically and comprehensively observe the development of the fetus, to check for congenital anomalies, to determine the position of the placenta, to measure the amount of amniotic fluid, and to observe the position of the fetus. The last ultrasound is near the due date, when the size of the fetus is measured again, the fetal position is determined, whether the umbilical cord is wrapped around the neck is observed, and the amount of amniotic fluid and the maturity of the placenta are observed in order to determine the mode of delivery.