Hi, I'm a big fan of your research and writing about labor and birth - you could say I'm a long-time reader, first-time poster...
I got pregnant at the beginning of January, and know within 7-10 days when I concieved. Because I am still nursing my two-year-old, and hadn't had a period to base my pregnancy off of, I agreed to an early dating ultrasound. I estimated I was around 6 weeks, 2-3 days when I had the u/s, and the actual machine dated me at 5 weeks, 5 days. The tech then went to a different computer and told me it would compute my "official" date, which was 5 weeks even. I was happy with the date (though I knew it was at least a week later than I really was), because I didn't go into labor with my son until 41 weeks 1 day, and am planning a VBAC for this birth.
I had my routine anatomy scan last week, and the tech/attending OB moved my due date from October 6 to September 22/24. I want to either keep my original due date, or only move it up a few days at most, as I want be able to go into labor on my own, and not be battling against a repeat c-section at the end of this pregnancy. I have an appointment with my midwife next week, so I don't know how hard and fast she plays by the rules regarding a changed due date, if at all, yet.
Can you point me to any research or literature about the accuracy of estimating due dates during mid-pregnancy? Any other advice about this situation is greatly appreciated, especially in regards to what I can do as a client in keeping or advocating for my original due date. Thanks so much!