Low fetal HR

Hi all-

I just left my “early sonogram” appointment.

Baby was measuring 5 days smaller (6.1 weeks) than what should be when compared to my LMP. HR was 77 which is low. Dr said baby could just be 6.1 weeks and my period was off, or it could be the start of a miscarriage. He’s optimistic but also aware of the risks.

Has anyone had a successful pregnancy with such a low initial fetal HR? I appreciate his optimism but can’t help but think it’s just to make me feel better. Next sono is next Thursday.