29 weks pregnant, my baby has 1.3 mm of water in his brain ( ventricles) im terified. how bad is this?

I went to the doctor yesterday to do a regular check up and an ultrosound of the baby and he said that the amound of water in the babys brain is abnormal. Normal is anything bellow 10.0 my baby measured at 10.3 (13). He didnt seem conserned had had the " whatever" face which angered me. I read some comments about this from diferent parenting sourcesces and most moms say that their babies measured at 12 but it usually goes down, however better brain scans are needed to examine the brain better. How common and bad is this and has anyone gone through this at this point of the pregnancy. Im going to the doctor tomorrow. Any help is apreciated. Thank you