While it's totally up to you, I can never pass up an ultrasound because I just love to see anything during pregnancies. A scan at 6 weeks will be internal, so keep that in mind. I've had three scans during the 6th week and a heartbeat was seen at all of them. I guess as long as you go in aware that you may not see a heartbeat yet then you won't be too disappointed if you don't see one. Apparently the earlier you have a dating scan the more accurate it is though. In the beginning babies grow at pretty much the same rate, then later on they start to grow at different rates.

But most importantly... Congratulations on your pregnancy!!!