I think its really important for the Mum to be properly informed about the limitations of Ultrasounds and the possibility of false positives and negatives. I have known of quite a few women who worried for the whole pregnancy about cysts on kidney or the brain, only for it to be normal when scanned after birth. On the other hand, an acquaintence of mine had a baby with Down syndrome and heart defects that were not picked up on ultrasound. She felt quite betrayed by this, understandably.
I can accept that for some couples it is a way of starting the bonding process (particularly for Dad) and does provide some degree of reassurance. Also even if there was some abnormality, for some parents I guess they can start preparing themselves physically and emotionally if they decide to continue the pregnancy.
A very personal decision about which parents have a right to be informed.