Hi everyone, I wonder if you can help me? My lmp date is 10/5/09 which would make my due date 14/2/10. I had a scan at 9 weeks and 4 days which changed my due date to 13/2/09 then at my 12 scan I was measuring 3 days ahead so changed my due date to 11/2/09. I am certain of the date I conceived (24/5/09) so how can the dates change? Is it based on how the baby is measuring?

Everything is an educated guess when it comes down to the "age" of a baby on a scan. When I pregnant with my son my due date according to my lmp would have been 7/14, a scan at 6 weeks said 7/31, scan at 18 weeks said 7/13. Usually there is a two week window because you can 2 weeks early or 2 weeks late. I ended up having my son on the 7/19-in the middle of the dates. Hope everything goes well for you.

The due date can actually vary by almost 2 weeks. Since it is impossible to tell when the sperm actually me the egg, we have to guess according to your LMP.

You are only talking about a couple of days here. You could deliver on any one of these due dates... two weeks before... two weeks after... or anywhere in between.