The abnormalities detected by ultrasound include some microscopic abnormalities (also known as potential markers of chromosomal abnormalities) in addition to the obvious severe abnormalities. There is a correlation between these microanomalies reported in the literature and fetal chromosomal abnormalities (mostly aneuploidy). Common microanomalies include: increased NT 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 anomaly, etc. 1.NT : NT is only the maximum thickness of soft tissue between the skin and fascia layers at the back of the fetal neck, reflecting the accumulation of lymphatic fluid in the subcutaneous tissue. Before 14 weeks of gestation, the lymphatic system of the fetus is not well developed, and some of the 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. The NT examination should be performed at 11-14 weeks, and the commonly used criteria for determining NT are ≥ 2.5mm at 11-14 weeks of gestation and ≥ 6mm at 14-22 weeks of gestation. This can be relaxed in advanced pregnancies. It has been reported that 10% of early NT widening is combined with chromosomal abnormalities, mainly trisomy 21, trisomy 18, trisomy 13 and Turner’s syndrome. In addition, non-chromosomal abnormalities 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 cyst (CPC): The choroid is located in the lateral ventricle, the third ventricle, the fourth ventricle, and is the site of cerebrospinal fluid production. c P C, which is a cyst in the choroidal plexus, is thought to be caused by folds of neuroepithelium within the choroid, containing cerebrospinal fluid and cellular debris, and can be single or multiple. C P C occurs in 1-2% of normal fetuses and may appear transiently, but disappears at 20 weeks. Most of them are 3-5 mm in size, and those found after 18 weeks with a diameter of 10 mm or more should be considered for diagnosis. The majority of these abnormalities are not combined with other parts of the body. The cerebrospinal fluid is produced by the intraventricular choroid plexus and enters the third ventricle via the interventricular foramen, then the fourth ventricle via the midbrain aqueduct, and then the subarachnoid space via the middle and lateral foramina. Various causes cause obstruction of cerebrospinal fluid circulation, accumulation in the ventricles, and ventricular dilatation. Significant ventricular dilatation with a lateral ventricular width of ≥15 mm is called hydrocephalus.