Ultrasonography during pregnancy reveals a fetal lateral ventricle diameter between 10mm and 15mm, which is medically known as mild fetal lateral ventricular widening. There are two types of cases: if the fetus has only mild fetal lateral ventricular widening and no other fetal ultrasound abnormalities are found, it is called “isolated mild lateral ventricular widening”, which may be on one side or both sides. If other abnormalities are also present, it is called “non-isolated mild lateral ventricular widening”. Mild lateral ventricular widening may occur in 1 – 22 out of 1000 children, and is often not caused by ventricular obstruction, and the child does not have elevated intracerebral pressure or brain compression atrophy. It may be a normal physiological variation of the child, but it may also be one of the early manifestations of chromosomal abnormalities, other possible abnormal brain structures, infection in the child in utero, bleeding in the brain, localized lesions, etc., so it is still important to pay attention to it. The percentage of children with chromosomal abnormalities is higher when the fetus has mild lateral ventricular widening (especially when the lateral ventricle exceeds 16mm), about 3% to 16%, and even when the lateral ventricular widening is not combined with other abnormalities, 4% of the children still have chromosomal abnormalities, the most common being trisomy 21 (also known as The most common is trisomy 21 (also known as Down’s syndrome), followed by trisomy 18, trisomy 13, etc., are children with serious deformities and disabilities, and if these poor children are not found to be born, it is too cruel to the child and the family, and the social family burden is too heavy. This is the reason why we need to do Down’s syndrome screening and fetal ultrasound screening during pregnancy. The proportion of children with mild lateral ventricular widening is somewhat higher in these chromosomal abnormalities, so most prenatal diagnostic centers have made it a priority to screen in the middle of pregnancy. About half of the fetuses with mild lateral ventricular widening also have other anomalies, such as central nervous system anomalies (e.g., spina bifida, agenesis of the corpus callosum, etc.), fetal cleft lip, congenital heart disease, abdominal cleft, and umbilical bulge. Most of the cases with a simple mild widening of the lateral ventricles without other abnormalities may be normal variants or may be early manifestations of other diseases. Approximately 1/3 of these ventricular enlargements resolve to normal during pregnancy and are more likely to resolve when the lateral ventricular width is < 13 mm. This transient widening of the lateral ventricles may be caused by temporary delayed drainage or overproduction of cerebrospinal fluid and is usually of little consequence to the child. However, about 8% to 16% of cases may develop in utero into severe lateral ventricular dilatation, which can affect the child's brain development. A further 4% of mild lateral ventricular enlargement alone has chromosomal abnormalities, mainly trisomy 21 (Down's syndrome). If mild lateral ventricular widening is suspected on ultrasound screening, a detailed examination for other structural abnormalities or ultrasound markers associated with genetic abnormalities is needed. A nuclear chromosomal analysis of the fetus is also recommended. Since lateral ventricular widening is also associated with intrauterine infection, TORCH Eugenics 5 virus screening is also recommended. Fetal MRI can rule out other fetal brain lesions. If there is only a simple mild lateral ventricular widening (isolated mild lateral ventricular widening), the current medical management recommendations are: to perform a systematic fetal ultrasound to look carefully for other complications and to look for soft markers of fetal chromosomal abnormalities. Perform amniocentesis or fetal umbilical vessel puncture, amniotic fluid or fetal blood sampling to check fetal karyotype and rule out intrauterine infection. Some specialists also recommend MRI of the fetus, which can better show whether the fetus has lesions such as ischemia or hemorrhage in the brain. If none of the above tests reveal any abnormalities, you still need to review the lateral ventricular changes periodically, have they disappeared? Is there any aggravation? Are there any new problems? There are still some children in whom other abnormalities are found during the follow-up process. However, even after the most detailed prenatal examination, about 10-30% of children with simple mild lateral ventricular widening are still found to have an abnormality that was missed prenatally after birth.