At 31 weeks, the width of the fetal cisterna magna is about 12mm. Is this normal?

Patient's question:

No

Doctor's answer:

Enlargement of the fetal posterior fossa cistern suggests the possibility of fluid accumulation. If the fluid volume is less than 10 millimeters and the fluid gradually decreases, disappears, or remains unchanged during regular follow-up, it is considered a normal variation with no significant impact on the baby's future development, and pregnancy can continue. For cases where the fluid range is between 10 to 14 millimeters, it is necessary to first rule out the presence of other malformations and chromosomal abnormalities (fetal cranial CT, umbilical cord blood).