What Are The Chances Of Losing Embryos?

Hi, may I answer your health queries right now ? Please type your query here...I had embryo transfer 13 days ago in tha meantime I had period so definitly I am not pregnant.when I had the procedure done the doctor said that are9 embryos left to freze.yesterday the hospital send a letter saying that I had no embryos frozen.I called hospital and at lab they said that they don't know what happened and to talk to a nurse.is it possible that they lost my envies?