Congratulations digi, just seen you got your BFP, so pleased for you 
I hope you ladies don't mind, but I was wondering if I could pop back and ask for some advice on dating of pregnancy (before I possibly make a pillock of myself...)? I'm not sure if my antenatal bunch were quite such avid charters but I have asked them the same questions.
I have my 20 week scan tomorrow and I am kind of expecting to be told my baby is "small" for dates, but actually I think my dating scan was about a week out.
As I understand it, actual pregnancy is 38 weeks from conception to birth? (to get to 40 weeks, they add 2 weeks that in theory takes you back to your period, assuming ovulation on day 14)
My dates were:
Period started: 31/05, lasted 5 days
Ovulated: 11/06, on CD12
Usually have 10 day luteal phase so was expecting next period on 21/06, got BFP on 24/06 at 13DPO
So, counting forward 38 weeks (or 266 days) from ovulation (assuming conception was that day, or possibly the day after) gives an EDD of 04/03/2011, which is the due date I originally worked out.
However my dating scan came up with EDD 25/02/2011, a whole week earlier, so I reckon there must be a margin of error/big baby??
To have an EDD of 25/02/2011 I would need to have conceived on 04/06, i.e. CD5 when I was still on my period. Surely this would be nonsense?
Does anyone have experience of arguing dates with the NHS?
Thanks