6 week ultrasound

My husband and I went in on Monday for our scheduled ultrasound after an FET at 6.5 weeks. Unfortunately the doctor couldn't see a baby, just the sac and yolk. She seemed pretty certain that something was wrong and told us that although it could end in a normal pregnancy, it'd more likely be a miscarriage. We had PGS testing done, so we know we're not dealing with any chromosomal abnormalities - and after reading other blogs and posts, I'm surprised that she seemed so sure instead of thinking it could just be too early to see the baby.