Hu, I have gone through your question. Enlarged ventricle in fetus is said when the ventricle size in second trimester is more than 10 mm. It can be increased in fetus with some nervous system anomaly or can also be increased in with fetus with chromosomal anomaly, especially Down syndrome. I would suggest her to consult a fetal medicine specialist and a detailed anomaly ultrasound doneto find the associated congenital anomalies, of present. Further management and amniocentesis, if required Will be done accordingly. The condition is fatal or not will be decided after these steps only. Hope you found the answer helpful. Wishing you good health.