How does it work with due date with very irregular periods? Lmp not reliable

[SunnySideUp2020]

My cycles (or rather the absence of them) could range from 45 to over 50 days long.
My LMP is 15 December. But I know for sure I did not conceive 2 weeks later. Perhaps 4.

I have my first gynaecologist appt on Monday but just really wonder how it's going to work going from here because I remember with my DD the only thing they ask is LMP at every single ultrasound until the end. Never the EDD.

Will I have to explain everytime? Are they gonna tell me "you measure small"?
What about the due date?

Are you in the uk? I also have irregular cycles and all of my initial due dates based off LMP were way off, but at the first scan they adjusted the due date based on being able to tell the age of the fetus from the scan somehow. No one asked me my LMP after my initial midwife appointment. I'm in England.

The 12 week scan is also called the dating scan for this reason.

I am Switzerland. Have no idea what it's like here... just moved.

@BewareTheBeardedDragon so they had your patient notes somewhere already?
Like in their system?

Hi, I ovulated late and as a result had an early scan because I wasn’t testing positive on any pregnancy test until what seemed like unusually late into the pregnancy. Then I could be sure I’d ovulated late, so every time at subsequent appts or scans when they asked for my LMP I gave it but immediately added “…but I ovulated later and these are the suggested ovulation dates!” At my dating scan the baby was properly measured & I have a due date based on my ACTUAL ovulation dates. Don’t worry. Just be prepared to do a little explaining x

@SunnySideUp2020 In the UK you get a copy of your notes to carry around with you to every appointment, I think so that wherever you are if you need any medical attention re. Pregnancy you have all the info right there. I know that the NHS does also have online records but I'm not sure how available they are in every hospital.

Obviously it will not be the same in Switzerland but it would be madness if they kept going by LMP after scans have begun since LMP is not a very accurate way to predict a due date. Maybe ask them? Sorry, not sure I've been very helpful since were in different medical systems.