Almost all of the internal organs of the fetus will continue to grow and change before birth, so it is not guaranteed that the organs that are in normal condition during the early examination will also be normal after birth. Because ultrasound is limited by the mother’s belly and uterus, it is not possible to adjust the position of the fetus, so it is not possible to obtain images from certain angles. The following are some of the limitations of ultrasound due to fetal growth conditions: 1. Hydranencephaly There are many cases of hydranencephaly or hydronencephaly that occur gradually in the second trimester of pregnancy. 2. The fetus will not open its eyes because there is no light stimulation in the womb, so it is not possible to diagnose congenital total blindness or microphthalmia. 3, hearing in the fetus 5-6 months old, hearing has developed, but there is no way to know, whether the fetus has congenital hearing problems. 4, congenital heart disease The atrial septum of the heart (i.e., the foramen ovale), as well as the ductus arteriosus, are gradually closed after birth. Although heart disease can be easily diagnosed at birth, it is not possible to know before birth. Obstruction of the gastrointestinal tract Obstruction of the gastrointestinal tract rarely occurs before the 24th week of pregnancy because the fetus rarely swallows amniotic fluid in the first trimester. 6, limb (fingers, toes) abnormalities such as inversion or ectropion of the hands and feet, polydactyly, syndactyly or missing knuckles and other abnormalities, but also because the fetus is often in the state of clenched fists, it is almost impossible to diagnose by ultrasound. 7, dwarfism Some of the symptoms of dwarfism can not be diagnosed at an early stage. This is because the fetus will gradually stop the development of bone growth when it is 6-7 months old. Inborn metabolic abnormalities Most of the biochemical metabolic abnormalities, such as Mucopolysaccharidoses, do not develop until after the baby is born and fed. Therefore, many lethal anomalies cannot be recognized before birth unless the mother has already given birth to a baby with a similar disease. The first ultrasound is performed in the 18th-20th week. It provides a general diagnosis of fetal malformations and observes the activity of the fetus. It can give a quick “answer” to those highly suspected fetuses, such as anencephaly, hydrocephalus, cerebrospinal bulge, umbilical cord anomalies, digestive tract anomalies, conjoined twins, microcephaly, and so on.