Scan due date accuracy?

[lou4791]

Does anyone have any up to date information on how accurate the 12 week dating scan is? I know it's meant to be very reliable, but surely there is room for human error?
I'm coming up to my due date by scan but not due for another 2 weeks according to my dates. My date was worked out by conception rather than LMP as was not having regular periods due to breastfeeding DS2 at the time. However , i'm really sure of the conception date as lovemaking has been a rare event since DS2s birth.
My dating scan made me 12+6, wheras I thought i was 11 weeks exactly. Beginning to think about what i'll do at the point induction is offered.
Any thoughts?

I too have nagging doubts about the dating scan. I'm now 40 + 7 but in my heart of hearts, I think I am more like 37 weeks. When I first went for my 12 week scan, I was told I was 15 + 6. Big shock all round! I am 99% sure of conception date and I also had a full period bleed during the time that the dating scan says I was pregnant. It's interesting that I've reached 40 + 7 and had no labour signs whatsoever. Can't help but wonder, but of course they won't change my dates and it's pretty pointless anyway. I guess there has to be leeway in these things and so long as they are not inducing you at a dangerously early time, then you should be fine.

I don't have any medical training so my opinions are purely based on my personal opinion.

I think that by approx 12 weeks a baby's growth is less easy to date than earlier scans. Once all the vital organs are formed the size of the baby varies more from baby to baby. By 12 weeks I think that using the size of the baby to determine due date is less accurate as there is a bigger range by then. I think you're right there is also room for human error. They may be able to re look at your dates at your 20 week scan, it could indicate if they were a bit out.

If you think your dates are way out it's worth putting your case to your MW and baring it in mind when it comes to discussing induction.

the other problem is that a normal pregnancy can be anywhere between, if i remember correctly, 37 and 42 weeks. so even if you do know date of conception, that doesn't necessarily tell you whether your, for example, 40 week baby is 'ready' to come or not.

ds1 i wasn't too sure on conception but had a scan at 5 weeks which is supposed to be incredibly accurate, and he came at 37 weeks based on scan, still covered in lanugo and looking premature.

ds2 arrived at 42 weeks to the dot from conception.

dd was a section at 39 weeks from conception, the only one i hadn't gone into labour naturally with, and she was in by far the best shape.

but if you don't want to be induced, there's no particular reason to do so until 42 weeks.

I am suffering from the same issue, except mine affects the date of my C section. So instead of 39 weeks (by scan) I think its 37 weeks. The consultant didn't care that my last 2 babies were over 10lbs so most likely it's a big baby not 2 weeks older. Nothing I could do

but hatchypom they can't force you into having a section if you don't want one?

with dc3 they wanted to do a section at 38 weeks because it suited the consultant's schedule better, but i wanted to leave it as late as possible, so that's what we did.

I think my due date was wrong with DS. I was induced at +10, he was born at +12, but he showed no signs of being overdue, I.e. no wrinkly peeling fingers etc. Throughout the pregnancy, I consistently measured 2 weeks smaller than dates. DS was 8lb 6ozs born, which seems a bit big, but I was expecting him to be big (I was 9lb 7ozs). So I'll be a bit more sceptical with this DC.

Absolutely we haven't agreed the date yet, but the 2 week difference between me and them does have an impact, as they don't let you go past due date.

My friend had IVF !! So she knows the exact date of conception and when she had her scan it was argued !! How can it be argued in a situation like that ! Very strange !!

I'm pg with an ivf baby and know the exact date of conception. At my 12week scan the baby was measuring 13+1 so it would have brought my due date forward by 8 days but I kept my oringinal date as I knew it couldn't be wrong. I'd say 2 weeks wrong either way would be an easy mistake to make depending on babies growth and slight human error. (20wk and 30wk scan also showed baby was at least 1week ahead depending on thigh/tummy measurement)

Yeah I was sure my dates were out with ds1 by 2 weeks. I had him at 42 weeks and despite being a whopper he was in no rush to come out.
My initial dates had me at 28th aug, scan said 19th and he was induced on 1st sept. No way was he 2 weeks over.
2nd dc scan tomorrow so we'll see what they say. I had a scan at 7.1 weeks so tomorrow should be exactly 12 but we'll see.

I just had my dating scan and it's brought my due date a whole week earlier than by LMP! I was charting and using OPKs so pretty much know when I ov'd and it certainly wasn't CD7? I'll also be booked in for a CS and don't want them to do it too early!

Thanks for the feedback.
I suppose it proves that dating scans aren't as accurate as we're led to believe, especially when differing from known IVF conception dates. This could have a real impact on how birth goes, with unnecessary inductions/interventions.
I hope my baby comes before 42 weeks so I won't need to decide whether to be induced or continue waiting for baby after the scan date 42 week cut off.

I'm a first timer so can't speak from experience. However I kind of feel if baby comes (naturally or not) some time after 37 weeks I'll be happy enough. I was certain of my Ov date (used the sticks). Dating scan put me at conception 5 days after positive Opk. But then 12 week scan put me at 1 day before positive Opk (we didn't dtd on that day). Anyhow, my dates are looking pretty spot on so I was very impressed at how accurate it was for me...

hatchypom
"they don't let you go past due date."

They are in no position to 'let' or 'not let' you decide whether you want to consent to an operation once you are informed about the risks and benefits of the procedure, they dont 'let' you.

Hi! I had a dating scan yesterday and they put me at 13+2 whereas I am pretty sure that I am 14+2- I don't understand this as I was charting, using opk's etc and am positive I know when I ovulated and this date puts me at 7 days past ovulation?! Also I used the CB digital conception tests each week to make sure my hormones were increasing as they should have been and those tests agree with my dates ... I told the scanner lady this and she said it's not an exact science... great! I suppose it's all irrelevant really unless you are being induced as baby will come when it wants too! xx