Our twins were both at exactly 6 weeks 0 days, but I have heard that in the early stages its totally normal to have them a few days apart ! I am sure if there was anything to be concerned about, your doc would want to see you sooner! We have our next scan in 3 weeks, which will be our 12 week scan, but have to go to the hospital for an antenatal appointment at 10 weeks. (I have a gigantic cyst in one of my ovaries, its about the size of a tennis ball - so I think they want to get me in sooner rather than later!!)
Just cant wait for the 12 week mark so we can announce, the secret is killing me!!