Was wondering how many words a 18month should be saying / how many yours said at this time?

DS was born 8 weeks early so corrected age is 16 months, but reached all his milestones at the same rate as full termers - walking, sitting up, etc and we were told that at 12 months we could stop going by corrected age.

However is about to be 18months and he has no words, mumma and dadda maybe but never really in the right context. he babbles, has full on conversations (flying hand movements and all) but there are no words that we can understand.

He does however have fantastic comprehension. If you say can you get the ....for mum, he goes and gets it, he gets scared when watching Thomas and the trains faces look worried, if you say where is your wiggles book- will go to the playroom and find it.

I have some other mums in my ear planting the seed of doubt that maybe we arent done with specialist and he is "delayed". I want to bury my head in the sand, but to be honest have no idea if its normal or not. Getting in to see a Paed here is town would take many months, prob would be quicker to go to brisbane if needed, but with a bubba due any day, its not practical for at least a month.

any advice would be great. TIA