baby stop growing

I am 8 weeks pregnant two weeks ago I was having break through bleeding went to ER and they did a vaginal ultrasound were dr's confirmed I was 6 weeks and had a strong heartbeat  at the time.  today I went in for my new OB visit and new ultrasound was performed showing I was only 6 weeks again and still saw a heart beat. How can this be and what does this indicate?    

[Yao Sun, MD, PhD]

You should discuss the ultrasound findings with your Obstetrician.  As a Neonatologist, I am not qualified to address all the possibilities for the ultrasound findings that you describe.