Dating scan

[firstbabyloading]

Hi all I am having my first scan tomorrow and was just wondering how the dating works, sorry if this makes me sound dumb. My lmp was 30th Jan which makes me 12 weeks 2 days, but i was tracking and know for a fact that I ovulated and conceived on 25th Feb which would make me around 9 weeks, is this what they will see on the scan as I'm overweight and worried they will struggle to see my baby if it is smaller than expected to be at 12 weeks? Shall I tell them I know the date I conceived? Sorry if this is stupid my 1st baby and got scan nerves thanks in advance x

They date by measuring baby's crown to rump length. I'm also overweight but they had no problems seeing baba as I had a nice full bladder. I am very irregular also so fully expected to measure behind at scan, and I did by about a week. But when they said I was measuring a bit behind I said I was irregular and that I wasn't surprised so since all looked healthy they weren't concerned at all! As long as they can see baba and heartbeat and you know yourself that you'd be a bit behind they won't be concerned. They'll just give you a later due date and either another scan or blood tests at a later date if you are too far behind for NT etc :)

It's done by measuring length of head spine feet legs. How formed the organs are ect. Had my first scan yesterday I was dated at 18 weeks not the 14 week I thought

I had my dating scan earlier this month and found I was 10+5, not around 11/12 weeks as possibly expected. Tbh I knew I’d ovulated a bit later in my cycle than average so I wasn’t surprised. I just had to go back a week later for another scan.

As others have said, they will date you purely on the measurements they take, they aren’t interested in lmp or ovulation.
I had a private scan at what should have been 10+3 based on my dates. Baby measured 10+2.
At my dating scan we gained 5 days! So my EDD was earlier. Even though when you look at when that makes conception it doesn’t add up. It’s the growth rate and therefore size of the baby that matters.
Good luck with the scan!

My periods are irregular so when they did my 12 scan they noticed baby was small and asked about my periods, I confirmed they were wobbly and they asked me to come back in a week or two to do it again.

We had two contraceptive failures within s few days so know when conception happened-ish.

If you conceived on the 25th Feb you'd be just over 10 weeks pregnant. They may ask you to come back to repeat measurements, especially if you want the likes of the nuchal fold checked. One of the points of the dating scan is to clarify the due date a bit better, as it's well known not every woman ovulates on CD14 (which is what your due date based on LMP assumes)