Had 2nd ultrasound today at 7.3 weeks. 1st ultrasound at 6.3 weeks there was only a yolk sac so rescheduled for a week later. today had an embryo measuring 5 weeks 6 days and a heartbeat that we couldnt measure. should i be concerned? is this viable?

A "yolk sac at 6.3 weeks" and an embryo detected with a heartbeat at "7.3 weeks" with a gestational age by ultrasound of 5w6d indicates a viable pregnancy, and the dates "6.3 and 7.3" are inaccurate, since ovulation was delayed and the pregnancy dates by ultrasound are reliable. Measuring date of pregnancy by "last menstrual period" may not always be correct.