Help me understand what happened at my dating scan!

I had a dating scan today, and the sonographer asked about my dates and LMP, etc. Then she said she thought I looked very early, about 3 weeks along.

I've been devastated all day. If this is true, then it's very bad news. I got a BFP almost three weeks ago! I'm unsure of O dates exactly, but if I was measuring 3 weeks, something is wrong. Either way, there was just a gestational sac - nothing else to be seen at this stage.

When I got home, I looked at my copies of the scan and info. It said my mean sac diameter is 7.91mm. When I googled this, I found information that says this would be about 5-5.5 weeks pregnant. Going by LMP, I should be 6w5d but I know I ovulated late and I don't have regular cycles - I'm just not sure how late, exactly. I also found that while you might see a yolk sac or more at about 5.5 weeks, the threshold for seeing the yolk sac is 8mm. So it may be possible it was just too early to see anything on the scan.

I've been having bloods done, and my hcg levels are doubling every 42 hours. My GP is happy with that, and tells me it's not over yet. I'm getting more blood results tomorrow.

I guess, I just don't understand why the sonographer would tell me she thinks I'm three weeks along, if the sac is measuring 7.91mm. That doesn't seem to make any sense, even mathematically according to the information I have read? Am I misunderstanding? I want to hope for the best, but I'm scared. :(

Sounds to me like she meant 3 weeks since conception, which would mean 5 weeks since lmp (your Dr would say 5 since lmp anyway). Because they assume every woman has a standard 28 day cycle and ovulates on day 14, they add on 2 weeks to the actual fetal age.

I think the same as Teeki - she was most likely talking about the age of the embryo, not the week of pregnancy which would be two weeks more. I think it all adds up alright if you look at it that way. Good luck xx

Lee, what ended up happening?

All good. I know answer. Sorry.