I went to a obgyn today and they told me that I had a missed pregnancy and there was a fetus but no heartbeat I started bleeding 1-28-2012 so I made a appointment to go to the obgyn. I just don't understand. I was 10 weeks pregnant and they said the baby measured 7 weeks so does that mean I was only 7 weeks not 10 weeks. Someone told me that u can start hearing a heartbeat until 12 or more weeks.

We could only guess what a doctor means, these are things you could have asked them. If the fetus stopped maturing at 7 weeks, then even at 10 weeks, it would still only show 7 weeks.
You can of course get a second opinion. What has your doctor recommended?