hehehe this is so freaky, I dropped hubby off at work today thinking about when this question was going to pop up again.

Simple, easy answer is to go by your LMP. While claimed to be accurate, ultrasound is often very inaccurate, I have heard plenty of cases of misdiagnosis and inaccuracies - it's so common. There is a great Australian book written by a leader in the industry about "Prenatal Diagnosis" by Lachlan De Crispigny (sp?) - which is a great read.

Remember - your body is completely unique, the figures and measurements in a scan are based on averages and stats. Both of my children came no where near their due dates and only 5% of babies are born on their due date.