What Causes Developmental Delay In A Child?

My son was born with afew problems,no waters for up72 hours ,passed first stool before birth,cord was wraped round his neck and he was resuscitied twice he didn t receive any special care.he has huge development delays and only able to say afew short words at most only able to make sounds but the doctors seem to think its my fault because he is not in nursery but I have been saying from day one something was not right.he is my 5 child and none of my other children have never had any delovpment problems