The fetal posterior cranial fossa pool is approximately 10 mm wide and is not a cause for undue concern. Fetal hydrocephalus is due to the fact that the fetus is still in a rapid growth phase, the fetal brain sometimes develops faster than the conduit system in the brain, and the brain produces cerebrospinal fluid significantly larger than the circulation capacity of the conduit system, and sometimes a slight dilatation of the ventricles is found. Therefore, it is not necessarily abnormal. Close observation and regular follow-up are recommended. Unless there is a more pronounced effusion, for example, more than 15 mm, which is the pathological state. If it is 10mm, it still needs to be given observation treatment. For mid- to late-term pregnancies, the posterior cranial fossa pool is usually <1 cm wide and >1 cm should be followed up closely. If the fetal posterior cranial fossa is >1.4 cm wide, antenatal examination should be performed. If the width of the posterior cranial fossa pool is not very obvious, and if it is maintained from 24 to 38 weeks, it is not necessary to worry too much, and follow-up should be done. If the posterior cranial fossa pool is 1 cm wide, it is considered to be a critical value for hydrocephalus and is not indicative of a problem. It is safe to consider regular review as long as it does not continue to rise. Pregnant women should drink more water, pay attention to rest, observe the condition of amniotic fluid, and actively review for absorption.