Hi Kate,

I had this scan done last Friday when I was 12w1d. The OB told me that the baby has to be at least 43mm in length to enable the scan to be performed (I saw him at 10.5w and were just under this at the time so the scan couldn't be done and we waited until our next OB appt). He also told me that there is a distinct window of opportunity in which to perform the scan and from memory, it was between 11 and 13w. As far as I know, 16w would be too late (don't quote me as I'm not sure!).

And you're right, your PG is counted from the first day of your LMP, not the first day of your missed period.

I think your GP might have been having a bad day!

HTH....