Microcephaly usually takes 24 weeks, or about 6 months, to be detected, so fetal microcephaly does not necessarily have to be detected in the late stages of pregnancy; it can be detected in the middle of pregnancy. The head circumference of the fetus at 24 weeks is about 22-24cm. If the head circumference of the fetus is found to be less than 3 standard deviations from the normal value during examination at this stage, accompanied by abnormal development of the five senses and enlarged ventricles, microcephaly is diagnosed. Therefore, microcephaly can be detected in mid-pregnancy, and it doesn’t have to be detected in the late stage of pregnancy. Microcephaly is mainly related to exposure to toxic substances during pregnancy and abnormalities in the number or structure of fetal chromosomes. The brain development of a fetus with microcephaly will be significantly delayed or even stopped, and even if the brain is able to develop completely, the weight of the brain will be lighter than that of a normal fetus. It is difficult to treat microcephaly at present. In order to reduce the burden on the family, the pregnancy should be terminated promptly after diagnosis. It should be noted that the measurement of fetal head circumference may be abnormal if the gestational week is not accurate or there is an error in the ultrasound measurement, which needs to be checked again to make sure. If there is no obvious developmental abnormality, there is no need to worry too much. It is recommended to pay attention to the regular diet during pregnancy and to take regular physical examinations.