The number of congenital malformations born in China ranges from 800,000 to 1.2 million every year, accounting for 4% to 6% of the total births in China, which has become a serious social public health problem. Prenatal ultrasound has become the most commonly used imaging tool in clinical screening for fetal developmental malformations due to its advantages of being non-invasive, convenient, inexpensive, real-time and dynamic. At present, the initial systematic ultrasound screening at 18-22 weeks of gestation can detect most of the fetal morphological and structural abnormalities. However, in addition to the obvious severe anomalies, ultrasound findings also include some microscopic anomalies (also known as potential chromosomal abnormality markers). There is a correlation between these microanomalies and fetal chromosomal abnormalities (mostly aneuploid aneuploid) reported in the literature. Common microanomalies include increased nuchal translucency 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, and small jaw malformation. Nuchal translucency thickness (NT): NT refers to the maximum thickness of soft tissue between the dorsal skin layer and the fascial layer 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 some 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. 16 weeks later, it is called nuchal skin fold thick. NT should be performed at 11-14 weeks. The sonographic picture shows a non-echoic subcutaneous layer in the neck. The commonly used criteria for determining the thickness of the nuchal skin fold are 11-14 weeks of gestation (≥2.5 mm) and 14-22 weeks (≥6 mm). 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 hygroma 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. In general, about 80-90% of NT abnormalities are transient lesions and the fetus is normal.