Very confused by the due dating process.

[Titchypanda]

Do the hospital measure the 40 weeks from cycle start or conception?

I'm pregnant through iui so know the exact date we conceived, but the growth scan puts me a week and a half further a long. I'm really confused as they also have the iui date. Does this mean that it's likely I'll go over the estimated due date or would it not make a difference?

Thanks!

Due date is approximate- it's +/- 2 weeks really. So prepare for arrival anywhere between 38 and 42 weeks.

Dating scans are measuring such tiny lengths, errors are easy. Again, it's a guideline and more to measure how your baby grows over time than to give a due date.

Generally the midwife will go on the first day of your last period for your initial due date, then when you go for your first scan (dating or 12ish weeks) it will be amended if need be based on baby's growth. They do say however that you should prepare for a delivery of up to 2 weeks either way of your due date as they're only really a guide, you may have ovulated early or late in your cycle and baby will come when baby is ready!

Mine was from the start of my last cylce, I know I ovulated later than normal (CD17) on a 28 day cycle but they weren't interested. The dating scan says doctors dates are correct and I go by that now but in the back of my mind I know my EDD is most likely a little later, but it's a few days so no biggie :)
I think it means you might go over tie due date technically but then again due dates are not really accurate, you could deliver earlier or later, I think it's really just an approximate because they can't tell you they don't know when you'll have your baby!