I've been thinking of making a thread about this too! So, I have no advice, but if you don't mind, here's my situation.
I thought I was seven-ish weeks, but they said the sonogram measured six weeks four days.
I'd montored my ovulation first by cervical fluid observation for a while and then also with those pee tests for the last two months before my BFP. However, I'm not entirely sure when I ovluated the actual month I concieved, because there was a discrepency. The day that cervical fluid observation indicated I ovulated, which also lined up both with what the test had said last month, and with what the cf observations had indicated over the past several months, I didn't get two equal lines on the test. However, I did take more than one that day, and the color of the test line changed in such a way (first darker then lighter? I can't even remember) that made me think I'd just missed the point where the lines were equal. But I kept taking the tests anyway, and two days later, two perfect equal lines. There was dancing on both days, and also the day before the first possible date.
Now, my observations suggested that I usually ovulated around day 16-17, and I know it's usually assumed to be 14 in a 28-day cycle. So the first day I could have ovulated was day 17, and the other one was 19. I pretty much felt like it couldn't even be possible, because there wouldn't even be time for implanting, but I suppose I don't know if my period would have been late (it never has, though, in 25 years). Could the issue be that the calculations are all based on the idea that I had to have ovulated on day 14?
Now, I don't really care about the due date, I just worry that something is wrong. I had spotting, which is why I had such an early sonogram. And then I had actual red spotting two days after the sonogram, so I went to the hospital and had another one. I asked if the heartbeat was good for almost seven weeks, and the doctor said was "GREAT!" very definately, but I don't know if it was just normal and she wanted to make me feel better, or if it might mean the baby is older than they thought.
They seemed very casual about the change, like it wasn't unusual or worrisome, but I wonder if they just assume I was wrong about my LMP. I did actually mean to ask the doctor this, but my last appointment was the day I had the red spotting, so I was too upset to remember all the questions I'd meant to ask.
Does it matter? Or is it just one of those things?