I had my dr appointment today to make it "all official"

My dr has given me a referral for a dating scan, I am sure of the date of LMP but she's given me a referral anyway. However she recommended that I wait until I am 10 weeks as the heart beat may not be detected before then, which will cause me un-needed panic (my dr is a lovely lady and I believe she's only given me the dating scan so I can see all is ok)

So, I know the earlier the better in terms of accurracy of dates, however I seem to recall having a scan with DS at around 7 weeks and we saw the heartbeat flicker really well. Is it neccessary to wait until 10 weeks?

Thanks