how accurate are 12 week scans?

[sarahjacksonxx]

Hi there!

This is my first pregnancy, i had my 12 week scan yesterday that showed i was 12 weeks 6 days making me 13 weeks today although that takes me back to the 16th dec and my normal period actually started on the 19th dec i have a normal cycle 26-28 days every month! i was just wondering how many days scans can be out by? Was told my due date is the 21st September with that due date i was also wondering if there was any way at all i conceived one or after the 9th jan making me ovulate late in my cycle or would an ultrasound pick up if i conceived later in my cycle? I'm so confused lol, i don't expect anyone to know the answer just a little bit of help would be great :) x

They can be inaccurate as they are measuring something tiny so very small differences make a big difference but having said that it's more likely you just ovulated later. The science lessons at school with the 'perfect' clockwork day 14 ovulation are fictional a lot of the time.

I'm sure I remember reading once that 2 different sonographers can get as much as a 15% difference between their readings, which would make a huge difference to the edd.

Personally I know they were out by 5 days (this is assuming I ovulated the same day as dtd otherwise it could actually be more) with DD. She was a happy accident and I know exactly when it happened. If the scan dates were to be believed then I ovulated 5 days before we dtd This time I can only go by my lmp and assume I ovulate in the middle of my cycle as there were 2 occasions that could have resulted in pregnancy (we were actually trying this time, just not very hard) but they moved my edd after the scan by a similar amount.

My first pregnancy they changed my due date by 4 days then at the 20 week changed it back to the original date. I figure babies come when they come so a due date isn't all that important just an estimate of when you need scans and appointmens

The date is important if you go overdue and they are insistent on inducing you as a result kiki. This time I've been told they'll let me get to 40+10 then they either want to induce or elcs me (I know I have the right to refuse both if I choose). If they have their dates wrong then they could be insisting on it earlier than necessary, and in those 5 extra days there is a good chance I would go into spontaneous labour which would be preferable to all parties.

Skinny I'm confused what you're confused about. The scan dates back to lmp also.

If the scan has dated you as 5th Oct due date then you conceived around 13th Jan. Which ties in with the dates you have.
Makes you 11+2 now

I know that Sootica, I said in my post I know I have the right to refuse. It doesn't stop them heaping the pressure on you though and creating a situation where it makes refusal very difficult. If it is possible to avoid the additional stress it brings then that would be in the interest of mum and baby. I know as I found myself in this situation last time.

I think that they got my dates wrong, I knew exactly when I had my last period.
I then went two weeks over ( but was probably three and half ) I had a giant baby.

kaytee87 12 + 7 is 13 weeks. The day after would be 13+1. 7 days classes as a week.

Just so we're not confusing op even more!