Dating from scans

[JackJack84]

Hi all according to my LMP & CRM from 12 week scan my due date is 20/11. However I had a private 16 week scan where the sonographer measured head circumference & this brought the date forward to 17/11.

I know it's a small difference & could change at the next scan. Just wondering out of interest if you would stick with the date from the NHS scan or go with the revised date?

My understanding is that scan dating is most accurate around 12 weeks because there’s generally less variation in baby’s size at this gestation.

Later on they tend to do their own thing a bit more and stick to a percentile which shows what’s normal for them.

If your LMP and 12 week scan matched then I would still with that date.

My private scan was out too, and I mentioned it to my midwife who said they tend to be out and to stick with the NHS date, so I'm using that one...

But the most accurate one will be your 12-week date; it's unusual for it to be updated officially after that as babies are quite standard at 12 weeks, before and after that they grow at different rates.

Yes the NHS will go by the dating scan. It's only an estimate anyway that's why they say from 37 weeks babies are full term and will let you go to 42 weeks. Some countries don't even do a due date but a due month as a baby rarely comes on their due date anyway

Thanks all, I'll stick with the original date even though, as you say @popcorndiva, they'll probably not come on that date anyway 😁

Who is the date for? If it’s for work/maternity paperwork then go by the 12 week/NHS date as that’s your official due date.

If it’s for you then don’t hang your hopes on one date-you’ve got a fairly narrow range there but put plus or minus at least a week either side to that

There probably won’t be any dating done at the 20 week scan

Dating is most reliable from the 12 week scan. They won’t change your due date after that.

Measuring the HC is actually quite tricky and can give a false date if not measured correctly. Im guessing you went for a sexing scan at 16 weeks? Whilst private scan shops are great for sexing scans and 4D pics they don't really have to take the time to make sure the measurement is spot on unlike your NHS scan.

Stick with your CRM

@Narwhalsh it's for work but I'll just stick with the original as it's not much different

@steakandcheeseplease it wasn't a sexing scan, it was a baby date scan at Ultrasound direct. The sonographer was actually the same one who did my NHS scan funnily enough! I only booked it as it was £45 & both my parents could come as well as my partner, so I didn't book it specifically for dating

work will go by the date on your matb1 form which is given to you by your midwife after your 20 week scan and is the date you were given at your 12 week scan.