not talking

my daughter is 19 months old and she has yet to say anything. i mean, NOTHING. not even doggie or mama. Its strange because she is soooo incredibly smart. she understands everything, understands and follows complicated commands. She has reached all other milestones about 3 months ahead (such as jumping, stacking, drawing, putting clothes on, she can even fold towels and put her laundry away when she feels like it) she is also very very good at communicating her needs in other ways. she does talk in jibberish, a lot of "a bab bah aa" sounds. but thats it.

is this something i need to be concerned about? if not now when should i get concerned.