Just had a dating/viability ultrasound (which I normally wouldn't do, but we just had a 21 week loss in August so I am a little nervous, ya know?!?!) and I am supposed to be about 9 weeks and the baby was only measuring about 7..... HR was fine (like 115) no one else seemed worried. I know I can't be certain when I ovulated but I do know when my lmp was, and had some implantation bleeding and I know when that was....
Should I be worried?
Gee. I don't know. With all of my losses, there hasn't been a heartbeat. I guess, whenever the dates have been off like that (in my experience) there wasn't a heartbeat and the woman had a missed miscarriage. For example, by the time I had my ultrasounds at 9 weeks or 11 weeks, the baby had stopped growing at 7 1/2 and there was not heartbeat. In your case, though, I honestly don't know. I would say to not worry about it yet. If you go again and there's growth and a heartbeat, I wouldn't worry.
If you are freaking out already, I would schedule another ultrasound in a couple of weeks. You can hear the heartbeat via doppler by 11 weeks, though. So...it's just a game of "wait and see." I'm sorry you didn't see what you expected at your appointment. That is incredibly frustrating.
Honestly if everything seemed on track for 7 weeks and baby had a strong heartbeat I'd be less inclined to worry or fret over the difference. Implantation bleeding can occur a lot longer than most websites say it can. I had implantation bleeding at 8 weeks with my 2nd, had an u/s and saw one gorgeous little bean in there.
I agree about the heart rate; if it is beating strongly that is a good sign. I think this is also a time to count on your HC provider. If you trust her/him and they are not concerned then let their experience / opinion steady your nerves. Also, I think you may be able to hear the heart beat earlier by Doppler depending on the positioning of your uterus (I heard mine at 10 weeks 1 day) if doing that provides comfort (it has for me).