10 mm is usually considered to be within the upper limits of
normalNormal saline flush for ventricular size (it is not considered to be hydrocephalus). If no other abnormalities have been seen on ultrasound, 8 mm is still considered to be within normal limits.
I'm sure your Obstetrician will continue to follow the pregnancy closely and measure the growth of the lateral ventricles. Some asymmetry of the ventricles is not uncommon, and is not alarming unless other abnormalities are found.