Single umbilical artery (SUA): 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 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 singly, but is not uncommon in combination with chromosomal anomalies and other malformations, and is seen in approximately 50% of children with trisomy 18 and 10%-50% of children with trisomy 13. Further fetal echocardiography is clinically recommended. 2. Echogenic intracardiac focus (EIF): EIF is an isolated focal echogenic spot 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 similar to that of the fetal bone (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, which in itself does not impair health or cardiac function, is a normal variant and is common in Asians. 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 is recommended. 3. short femur length: long bone dysplasias 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 at the appropriate gestational week, but other growth indicators are normal, this is a high priority. 19% of trisomy 21 children have short femurs. 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, infants younger than gestational age, and congenital proximal femoral defects (PFFD). 4. hyperechogenic bowel: 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, 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 abnormalities, intestinal obstruction, meconium peritonitis, cystic fibrosis, intra-amniotic hemorrhage, and intrauterine infection. 5. Increased or decreased fetal eye spacing: The orbital distance between the eyes is too large or too small, commonly due to some anomalous syndrome. A rough estimate of the orbital center distance (mm) is approximately equal to the number of weeks of gestation and can be judged accordingly. When the canthus index is ≥38, the canthus index is too large, which can be seen in trisomy 13, trisomy 18 and trisomy 21; when the canthus index is <20, the canthus index is too small, which can be seen in forebrain holoprosencephaly, juxtacranial malformation and microcephaly, which are often also manifestations of trisomy 13 and trisomy 21. 6, nasal hypoplasia and absence of nasal bone: fetal nasal bone starts to develop in the 6th week of embryonic period, and ossifies in 9-11 weeks by membranous osteogenesis, 1.4% of normal fetuses have absent nasal bone. In approximately 50-60% of trisomy 21 children, nasal bone defects are detected on ultrasound screening at 10-14 weeks. Fetal nasal widening or narrowing can also be seen in a variety of chromosomal abnormalities. For example, anterior anencephaly and ocular hyperfusion in fetuses with juxtacranial anomalies may manifest as single nostril, elephantine nose and abnormal nasal position. The standard measurement plane is the median sagittal plane in the horizontal position of the fetus, which shows a thin line of strong echogenicity in the nasal bridge. It is important to note that nasal bone defects can occur in a small percentage of chromosomally normal fetuses, and the background prevalence of nasal bone defects in chromosomally normal populations depends on the ethnicity and facial features of the parents. 7. Increased or decreased distance between the corners of the fetal mouth: the distance between the two corners of the fetal mouth correlates with gestational age. The increased distance between the corners of the mouth is 2 standard deviations higher than normal and is seen in a variety of chromosomal abnormalities. The distance between the corners of the mouth decreases and is lower than 65% of normal fetuses of the same gestational age, which is also often a clinical manifestation of chromosomal and genetic syndromes. 8, fetal mandibular developmental malformation: no mandible (agnathia) or small mandibular malformation (micrognathia/micrognathism/small jawz/small chin) is often one of the frequent abnormalities of chromosomal anomaly syndromes. The fetus with micrognathia has a reduced anterior-posterior and left-right diameter of the mandible, which is significantly lower than that of a normal fetus of the same gestational age. Ultrasonography can clearly show the horseshoe-shaped mandible. In the past, visual inspection of the facial contour was more subjective, but now the jaw index is more commonly used to determine this. The mandibular index (jaw index) = (anterior-posterior mandibular diameter / biparietal diameter) × 100. mandibular index <21 in small mandibular deformities, commonly seen in trisomy 18, trisomy 21, 45XO, 5P deletion, etc. Chromosomal abnormalities have been reported in about 66% of small mandibular fetuses, and 80% of triplet children have small jaw anomalies in autopsy reports. 9, amniotic film: ultrasound examination during pregnancy reveals a strong echogenic band of light floating in the amniotic fluid, called amniotic film also called uterine cavity adhesion folds (uterine shelf). This is caused by the presence of adhesion scars in the uterine cavity and the growth of amniotic and chorionic membranes along the stretched scars. The echogenicity is strong and obvious because it contains two layers of chorionic villi and two layers of amniotic membrane and is thick. The incidence has been reported in the literature as 0.6%, although it is not uncommon in recent years and should be related to the increasing number of uterine operations in women of childbearing age. Amniotic slices are not adherent to the fetus and are not associated with fetal malformations, and no special treatment is indicated. However, care should be taken to differentiate it from other intrauterine band echoes, such as amniotic band syndrome, incomplete longitudinal uterine septum, contoured placenta, and amniotic sac separation in multiple fetuses. The causes of fetal anomalies are diverse, and there is no effective prevention method in medical science, but only through early diagnosis and timely termination of pregnancy. Ultrasonography is the first choice for early diagnosis of fetal anomalies. Some of these microscopic anomalies appear early and persist, some are transient, some appear irregularly, and some are late onset lesions. Although many fetuses with chromosomal abnormalities do not show any signs on ultrasound images. However, as soft-markers of chromosomal abnormalities, they can provide clues for careful screening of fetal anomalies and alert the operator to scrutinize the fetus for combined abnormalities elsewhere. For continued pregnancies, the sonographic changes should be reviewed periodically. Although the probability of problems occurring in the isolated presence of the above-mentioned phenotypes is small and the sensitivity and specificity are not high; however, for those pregnant women who are older and have abnormal serologic screening results (PAPP-A, α-FP, β-hCG, uE3, inhibin-A) and combined with other high-risk factors, chorionic villus biopsy (10-14 weeks) and amniocentesis (16-24 weeks) should eventually be performed in addition to MRI. In addition to MRI, fetal cells should be extracted by interventional methods such as chorionic villus biopsy (10-14 weeks), amniocentesis (16-24 weeks), and umbilical cord puncture for karyotype analysis to clarify the diagnosis.