due dates?

[OTTMummA]

Hi, just wanted to know roughly how accurate the 12 week dating scans are?
I know the first day of last period 19th october, and my cycle is about 28-30 days long, i tested on the 22nd november and got a BFP, my dates put me at 25 july, but gp said, 27th and mw said 26th! am wondering why they have come up with different dates, and whether or not the scan will come up similar dates or 1 week either way?
So any of you ladies knew your dates and the scan confirmed them, or was it completley out?

oh, and have my scan on the 10th, so will find out then i suppose, i was just wondering why we all came up with different dates when presumably using the same formula?

The scans are supposed to be very accurate, but I am not that convinced, I have heard a lot of stories of scan dates being clearly wrong. With DS my scan date suggested I conceived 3 days before I ovulated, when DH was out of town . A friend of mine has just had be be rescanned as the baby was "too curled up" to measure, surely any differences in curling can give you a different measurement, and we are talking mm here making days difference.
All that said, a 2 day window really isn't worth worrying about. Even when you know the dates the baby can still naturally arrive between weeks 37 and 43. I always think it's good if the date is a little on the later side, as it takes the pressure to induce off.

Oh and I expect your GP/MW are using a calendar or wheel that doesn't take account of cycle length/long luteal period or something like that.

I will be having a section, so would like to know thats all.

With DS my first scan was at gone 22wks so a bit less accuret i believe, and they placed him a week ahead of what i thought he should be, had a section at 39wks and he was perfect, not problems at all, so i always consider him to of been born on his due date tbh.

I'm just gettting excited and nervous thats all, only a few days to wait!

Or one for the wrong year that doesn't take into account the fact its a leap year. Its only a day (MW's date) so I really wouldn't stress about it.