Trisomy 13 with good ultrasound

Today I am 14 weeks pregnant with our first baby. When I went into the doctors for our 12 week appointment, my doctor drew blood samples from me to do the genetics tests (since Ill be 35 by the time the babe is born). Two days ago my doctor called me with some bad news. The Genetics result came back being positive for Trisomy 13. My heart dropped. Of course I took to google as soon as I got off the phone with the doctor, I didnt quite understand completely what this meant. Although I had read that it is possible that the genetics blood test can be a false positive, I was still very upset. The next day I had a phone call from a specialist that my doctor referred me to and they scheduled me to come in for a detailed ultrasound that day. Two different people (nurse and doctor) performed the same detailed ultrasound (that was comforting to have 2 sets of expert eyes) . Both said that the baby looks beautiful. No signs of T13. They look at everything! The brain, heart, stomach, kidneys, eyes, hands, feet, spine.... everything. This doctor said after the ultrasound he sees no reason to do an amneostesis yet, that since there is a 1/300 chance of miscarriage due to an amneostesis, he sees no reason to do one yet since there are no physical signs of T13.

Has anyone out there had a Normal looking ultrasound after finding out they were positive for Trisomy 13? Im waiting to hear if my normal doctor will still want the amneostesis done to confirm the teisomy 13.