<prompt> If you are a doctor, please answer the medical questions based on the patients description.I had an ultra sound at 4 weeks 6 days and nothing could be seen, just 3 small dots. I had another ultra sound 1 week later at 5 weeks 6 days and they only saw a very small gestational sac measuring at 3.51mm. The dates are exact because i had an IVF so we know the exact date of ovulation. Everything I read online says that by 6 weeks my gestational sac should be at 14mm, but mine was only at 3.51! Does this sound like I may be in for a miscarriage?  <response>: HI, I understand your concern. Average size of gestational sac at 5 weeks is 2-3 mm. After IVF assessment of the embryo size with USG alone is not considered reliable blood Chat Doctor levels are more confirmatory . As proportional Chat Doctor levels with trans abdominal detection of an embryo is sufficient to assess pregnancy by IVF in early weeks. Please dont worry follow your doctors instructions be positive. Thanks. 