Common microscopic anomalies include increased cervical hyaline layer width, choroidal plexus cyst, ventricular dilatation, widened renal pelvis, single umbilical artery, intracardiac strong echogenic spot, short femur, strong echogenic intestinal canal, nasal bone anomaly, small jaw malformation, etc. 1, cervical hyaline layer width: NT refers to the maximum thickness of soft tissue between the skin layer and fascial layer on the back of the fetal neck, reflecting the accumulation of lymphatic fluid in the subcutaneous tissue. The fetal lymphatic system is not well developed before 14 weeks of gestation, and a small amount of lymphatic fluid collects in the lymphatic sacs or lymphatic vessels of the neck, forming NT. after 14 weeks, the lymphatic system is well developed, and the accumulated lymphatic fluid rapidly drains to the internal jugular vein, and NT disappears. after 16 weeks, it is called the thickness of the skin layer of the posterior cervical folds. the time of NT examination should be between 10 and 14 weeks. The sonographic presentation is an echogenic subcutaneous layer of the neck. The commonly used criteria for determination are ≥2, 5mm at 10-14 weeks of gestation as abnormal; ≥6mm at 14-22 weeks as abnormal. The criteria may be relaxed in advanced age. Genetics, anatomical abnormalities or infections leading to lymphatic reflux disorders are the causes of NT widening, and some of them may develop into cervical lymphatic hydrocystic tumors by mid-pregnancy. It has been reported that 10% of early NT widening is combined with chromosomal abnormalities, mainly trisomy 21, trisomy 18, trisomy 13 and 45X0 (Turner’s syndrome). In addition, non-chromosomal anomalies such as cardiac anomalies, fetal edema, thoracic dominant lesions, skeletal dysplasia, and recipient of twin-birth transfusion syndrome should be excluded. Overall, about 80%-90% of NT abnormalities are transient lesions and the fetus is normal. 2. choroidal plexus cysts: the choroid is located in the lateral ventricle, the third ventricle, and the fourth ventricle, and is the site of cerebrospinal fluid production. cysts in the choroidal plexus are thought to be caused by folds of the neuroepithelium within the choroid, containing cerebrospinal fluid and cellular debris, either singly or in multiples, and can cause ventricular dilatation if the cerebrospinal fluid circulation is blocked. The incidence of CPC is 1%-2% and may appear transiently in normal fetuses but disappears at 20 weeks. The diagnosis should be considered in cases with a diameter of 10 mm or more found after 18 weeks. The chance of chromosomal abnormalities in simple CPC is in the range of 1 to 2, 4%. Simple CPC disappears in late pregnancy and in the vast majority of cases it is not combined with other abnormalities. If combined with other abnormalities, especially multiple malformations, the chance of chromosomal abnormalities is high, including trisomy 18, trisomy 21, etc. 3. Ventricular dilatation: Cerebrospinal fluid is produced by the intraventricular choroid plexus and enters the third ventricle through the interventricular foramen, then flows into the fourth ventricle through the middle and lateral foramina, and then enters the subarachnoid space through the middle and lateral foramina. Various causes cause obstruction of cerebrospinal fluid circulation and accumulation in the ventricles, resulting in ventricular dilatation. A significant ventricular dilatation with a lateral ventricular width of ≥15 mm is called hydrocephalus. It is mostly due to stenosis of the midbrain conduit, and the causes include chromosomal abnormalities of the mass, inflammation, and mass compression. After 20 weeks of gestation, lateral ventricles or cerebellar medullary pools with a width of more than 10 mm should be alerted to ventricular dilatation hydrocephalus and should be followed up closely. When the width is >10mm and <15mm, it is called mild ventricular dilatation. The incidence is 1.5-22 per 1,000, mostly not due to obstruction of the ventricular system. Further detailed examination of extracranial lesions, such as agenesis of the corpus callosum and cardiac malformations, should be performed. Note that about 5-10% of fetuses with isolated mild ventricular dilatation are chromosomal abnormalities, among which trisomy 21 children are more common. The posterior cranial fossa pool widening: also known as posterior cranial vault pool enlargement, Magna's bursa enlargement, refers to the distance between the fetal cerebellar pool and the anterior-posterior diameter of the medial aspect of the skull ≥ 10 mm. posterior cranial fossa pool widening is associated with fetal haploid abnormalities, especially trisomy 18, and is also seen in arachnoid cysts, Dandy-Walker malformation, etc. In the absence of other coexisting anomalies, ultrasound and other imaging studies may be performed for follow-up. 5. Renal pelvis dilatation or pelvis separation: Urinary tract obstruction leads to urine retention in the renal pelvis and calyces, and ultrasound shows dilatation of the anterior and posterior diameters of the renal pelvis. Severe renal effusion can cause atrophy of the renal parenchyma and increase the size of the kidney. Pelvic effusion has been reported to be detected in 2%-2.8% of normal fetuses and 17%-25% of children with trisomy 21. Fetal anomalies may occur with anterior and posterior diameter values of separated renal pelvis ≥4 mm at 15-20 weeks, ≥5 mm at 20-30 weeks, and ≥7 mm at 30-40 weeks and should be followed until after birth. Other organic lesions include pelvic ureteral junction stenosis, ureteral bladder junction stenosis or ureteral dilatation due to vesicoureteral reflux, posterior urethral valves, Prune-belly syndrome (urethral obstruction resulting in a huge fetal bladder with extremely thin bladder wall and fetal abdominal wall), etc. 6.Single umbilical artery: The normal umbilical cord contains two umbilical arteries and one umbilical vein. sua means that there is only one umbilical artery, the incidence is about 1%, and the absence of the left side is more common than the right side. The larger one is the umbilical vein and the smaller one is the umbilical artery, which is slightly larger than the normal lumen. SUA can occur unilaterally, but is not uncommon in combination with chromosomal abnormalities and other malformations. 50% of children with trisomy 18 and 10%-50% of children with trisomy 13 have SUA, and recently there have been reports of a significantly increased risk of cardiac malformations, renal malformations and IUGR with SUA. Further fetal echocardiography is clinically recommended. 7. Intraventricular strong echogenic spot or intracardiac focal strong echo: EIF is a point-like isolated focal echo on a four-chamber cardiac image, in the free area of one ventricular cavity, corresponding to the papillary muscle or tendon area, with an echogenic intensity approximating that of the fetal skeleton (rib cage). It may be solitary or multiple, with the left ventricle being the most common, gradually diminishing with increasing gestation and disappearing by the age of 1 year at the latest. It may be associated with inflammation, thickening and calcification of the papillary tendon cords, but it is a normal variant and is common in Asians, without impairing health or cardiac function. The incidence of EIF on ultrasound at 18-22 weeks of normal gestation is 2-5%, with a risk rate of 16%-30% in trisomy 21 children and 39% in trisomy 13 children; EIF with other ultrasound abnormalities increases the risk; alone, the chance of fetal abnormalities is low; the incidence of fetal chromosomal abnormalities with EIF is about 1/600 when the maternal age is ≥31 years. Echocardiography. 8. Short femur: Short long bones are considered to be one of the characteristics of chromosomal abnormalities, and the femur is the only long bone routinely measured by obstetric ultrasound scan. If the femur is measured to be less than the fifth percentile of the corresponding gestational week while other growth indicators are normal, it is important to take it seriously. 19% of trisomy 21 children have short femur. With a BPD/FL greater than 1,5, 54%-70% of trisomy 21 children can be detected. Short femur in middle and late pregnancy is also seen in chondrodysplasia, IUGR, less-than-gestational-age children, and congenital proximal femoral defects. 9. Intestinal strong echogenicity: not a disease but a sonographic manifestation, refers to the enhanced echogenicity of the fetal intestinal canal, the intensity of which is close to or higher than that of the bone echogenicity similar to that of the fetus, commonly found in the small intestine of mid- and late-pregnancy fetuses and in the colon of late-pregnancy fetuses. The incidence in mid- and late-term pregnancies is 1%. Most fetal follow-up results are ultimately normal, but a significant proportion of fetuses are confirmed to have abnormalities, such as chromosomal abnormalities, gastrointestinal malformations, intestinal obstruction, meconium peritonitis, cystic fibrosis, intra-amniotic hemorrhage, and intrauterine infection.