Which due date to use?

I'm confused to which due date to go by.

My last period was 18 or 19th October. So the due date for that is the 25th July. I believe I ovulated on the 2nd Nov and the deed was done on the 2nd Nov.

8 week scan put me due at 1st Aug.

12 week scan put me at 30th July.

Scan at 19 weeks put me at 6th Aug.

The OB said they can be out by a week, but it still puzzles me.
Do other people find this when they have scans?
I worry that at my last scan I was measured earlier because I haven't eaten enough or put on weight therefore baby too small. Any thoughts appreciated.

I ovulated on day 22 so Fertility Friend and my MW said my EDD would be 20th October.
I had a scan last week and baby was measuring exactly 8 weeks which is correct according to my LMP.
I asked what the chances are of that being wrong and she agreed that the earlier scans are the most accurate, so now my EDD is 14th October.

BTW 30th July is when all the great people are born *ahem*

Your mw will probably discuss amending the date at your next visit. I'd go with 1st August, it's kinda in the middle and means your hopes on the 20th July won't be too high

The earlier the scan, the more accurate. Scans at 8 weeks are 1-2 days out, at 12 weeks up to a week, and from then on can be 1-2 weeks out.

They usually choose an early scan EDD over a LMP EDD too as I found out last time.

And no, your baby generally will not be smaller because you haven't been eating. Basically the baby will suck everything it needs from you and leave you with no reserves if it really has to!

The 7 to 9 week scans are the most accurate ones and I will go with that due dates. That is what my gynae in SA said. After that it is more difficult to get accurate readings and babies start developing at their own paces. After 10 weeks they can be a bit out, depending on the person doing the scan and how old the equipment is and the babies develop differently.