positive screening for trisomy 18

Today I am exactly 12 weeks and although I should be beyond excited I am also sad and confused. Last week my doctor called me and said that I tested positive for trisomy 18. I have read of many cases where woman screen positive but then further test show that everything is normal. Next week we have an appointment with a genetic counselor and although I am trying to be positive I am so scared for my little girl. Has anybody gone through this?