Estimated Due Date - which is more accurate?

[Bunny2021]

My EDD was estimated at 28 July at my 12 week scan.

I had a private 4D scan at the weekend and it has my EDD as 28 July but there is also another date that has EDD(AUA) as 17 July. Does anyone know which is more accurate?

I've tried looking online but I'm not really following much of the advice. Thanks!

My understanding (not a radiographer!) is that EDD (AUA) is calculated off of the growth measurements of the embryo/foetus as seen in the scan and so is likely to be closer to accurate than an EDD based off of your last menstrual period date, which simply assumes you have a standard 28 day cycle with ovulation on Day 14.

@queenatom - thanks! That brings things forward a bit...need to get a little more organised!

OP if you are in the UK, the NHS will take due date as per your 12 weeks scan, and keep to that no matter how your dates progress through pregnancy (Ie measuring big or small by dates). LMP (last missed period) is only used as an estimated predictor until the 12 week scan!