Microcephaly usually takes about 24 weeks, or 6 months, to be detected, usually under ultrasonography, and the diagnosis becomes easier with increasing gestational age. The fetal head circumference is about 22-24cm at 24 weeks. When a pregnant woman’s maternity examination reveals that the fetal head circumference is less than 3 standard deviations from normal, combined with abnormal development of the facial features and enlarged ventricles, microcephaly can be diagnosed, but when there is only one condition of a smaller fetal head, it usually cannot be used as a diagnostic criterion. The causes of microcephaly include infection during pregnancy, exposure to toxic substances, and abnormalities in the number or structure of fetal chromosomes. In microcephaly, the development of the brain is significantly delayed or even stopped, and even if the brain can be developed, the weight of the brain is significantly lighter than that of a normal fetus, the brain gyrus is too small or there is no brain gyrus at all, the top of the newborn’s head becomes small and pointed, the bridge of the nose is sunken, the ears are large, the lower forehead is retracted, the forehead is narrow and the head circumference is extraordinarily small, the maximum is less than 42 cm. The physical development is obviously abnormal and the intellectual development is significantly delayed. Fetal microcephaly is difficult to treat, so to reduce the burden on the family, the pregnancy should be terminated promptly after diagnosis.