odds for ultrasound

Bunny • ttc 4 years with 2miscarriages. Rainbow BABY GIRL born 3/10/18💕🌈 Gorgeous girl#2 born 02/19/19💕💕 baby #3 due 03/01/21

i have a regular 28-29 cycle which puts my lmp at 6w6d when i get my ultrasound. i also got an early positive at 8-9dpo. what are the odds that baby will measure big enough to show heartbeat