34 weeks fetal posterior cranial fossa pool widening 1.0cm need to further observe the fluid changes to determine whether it is normal. 1. 34 weeks fetal posterior cranial fossa pool widening 1.0cm, within the normal range, need to continue to observe, if there is no significant growth on the fetus generally have no effect. 2. If the posterior cranial fossa continues to widen, or even exceeds 1.5cm, this condition will have a great impact on the fetus, which belongs to fetal hydrocephalus, and the possibility of fetal malformation is relatively high, and further magnetic resonance imaging is needed to confirm the diagnosis. Once the diagnosis of fetal malformation is confirmed, it is necessary to induce labor if necessary to avoid the birth of malformed fetus. The widening of the posterior cranial fossa pool by 1.0cm at 34 weeks must be followed up regularly under the guidance of the doctor, who will formulate an individualized treatment plan according to the specific condition, so as to avoid delays in the condition.