Original date given was 18 December but at the scan it was moved to 31 Dec. It just doesn't quite add up by my reckoning of when I think I ovulated and when I know we did the deed!
Unless you have an early pregnancy scan most of you will be given your estimated due date at the week scan. Of course you have probably already used an online due date calculator. This is where you discover that your due date isn't based on the date you conceived, it's actually calculated from when your last menstrual period started your LMP. It's because it gives a definite date for health professionals to work with.
There would be so many variables if it was calculated from when you think you conceived, especially as everyone's cycles are different and the fact that you don't necessarily conceive on the day you have sex! But this will only give you a rough idea. This is especially true if you have an irregular cycle or have been on the Pill for example. Experts say that the scan date can sometimes come out as less pregnant than suggested by your LMP.
But then again with my first baby I was spot on with dates, he always measured big and he was a week overdue Babies are ready when they're ready - try not to worry easier said than done. The healthcare professionals will stick to this date as far as possible because it is then used as the baseline for growth throughout pregnancy.
Your baby's growth can slow down and then have spurts. I've not even had my 20 week scan yet. I have scans every few weeks so it will probably keep on changing. My baby will come when it's ready anyway, maybe weeks before or maybe weeks after my due date. These can be carried out from week 5 or 6 of pregnancy, which is a notoriously tricky time to be accurate on dates.
Measurements at such an early stage aren't accurate which is why they wait for 12 weeks to date you. We always recommend mums get a definitive dating scan closer to 12 weeks as this will be much more accurate.
Just half a millimetre at such an early stage can change your date by a week. Your week scan will be far more accurate. The sonographer then said that I was only about 4. Then at the week scan I got an EDD of 15 march, so that early scan was completely out. Well, you'd think so, wouldn't you. At around 12 weeks you can get more accurate measurements. By talking to the health care professionals you should get a clearer picture as to what is happening.