The yellow card does help if you present to hospital for the EDD and where you were up to with your BP etc. We also send you to the Birthing Unit most of the time after 20 weeks but before that you are seen in Emergency (so the date is REALLY important then - and they don't like to believe the mum, just the card )

My DH was highly entertained by me being "yellow carded" at 8 weeks!!! He said you can't get anywhere without that card, and to some extent he is right