Then i can't read 8-12mV with my ardunio am i right ?
You can read it but the resolution is not enough for a serious application, so it simply doesn't make sense. You can amplify the signal with an op-amp (p.e. lm358).
I guess you next question will be the schematic you need for this. To be able to provide useful suggestions you have to provide the datasheet of the sensor. So ask the company for that and post it here.
What do you use that sensor for? It's a medical sensor but I hope you don't use it in a medical environment with connected to an Arduino.