The width of the posterior horn of the lateral ventricle is an important predictor of the development of fetal neurological function, and the normal value of the width of the posterior horn of the right and left lateral ventricles of a 5 1/2-month-old fetus is usually no more than 10 mm. With the increase of pregnancy, the inner diameter of the lateral ventricle will decrease. If the width of the posterior horn of the lateral ventricle of the fetus is more than 10mm, it is usually due to the abnormal growth and development of the fetus, which leads to excessive cerebrospinal fluid, abnormalities of the central nervous system, or it may be related to viral microbial infections or the presence of chromosomal abnormalities. If a pregnant woman finds that the width of the posterior horns of the right and left lateral ventricles of her 5.5-month-old fetus is more than 10mm, it is recommended that she should consult a doctor in time. Under the doctor’s guidance, she should complete the relevant examinations to ascertain the degree of dilatation of the lateral ventricles, whether there is any combination of other structural abnormality of the cranium, and whether it is accompanied by any other malformations, and take corresponding treatment measures.