13 month old twins no "real" spoken first words yet?

I started sign language with my daughter at about 13 months old. When I was teaching her myself she picked up the signs slowly and it took her a while of me doing them for her to get it. I bought her a sign language DVD called "Baby Signing Time" and she really started to pick it up quickly. All of the signs used are the real ASL signs. Within a week she knew about 10 signs from it and learned a new one each day. After about three weeks of watching the same DVD she knew all 25 of the signs and also started to speak the words as she signed them. Before that she had only ever said "baba" and "dada". She is now 17 months and I have bought all four of the DVD's in the series and she knows about 60 signs and speaks about 30-40 words. Most all of the words she speaks she also knows the signs for and does them together. There are a couple words that she learned to speak without knowing the sign and so I taught her the sign on my own and she now uses them together although not as often as the words that she learned signs for first. I would suggest buying one of the DVD's and see if they like them. I really think they helped my daughter learn to start speaking as well as giving her a good introduction to sign language. The first DVD in the series teaches the most helpful words like milk, juice, cracker, potty, hurt, where, all done, and many others. Each DVD has about 25 signs and I absolutely love them!