I am in exactly the same position as you. I was 36 weeks and had a growth scan done because i was measuring 4 weeks bigger then what i was. The growth scan came back as my baby being the size of a 39.5week baby but they did not change my due date currently at 14/04/2008. I have worked out when my last period was and going by that I should be due any where between the 08/04/2008 and the 14/04/2008 so the scans are not accurate by any means.

My baby's HC was measruing at 37cm and the weight 7lb 8 ounces but even the midwife said that may not be accurate.