I want to go by the ultrasound because it matches when i ovulated better than my last menstrual cycle. My Dr goes by the last menstrual cycle.
If the doctor does an early ultrasound to date the pregnancy, at 9 weeks or before, that is usually very accurate.
If you don't have a dating ultrasound, the last menstrual period is the most accurate marker. If you don't have either or those things - an accurate memory of the last menstrual period, or an early ultrasound, it's much harder to guess correctly.
Usually the first due date a doctor gives you is most acurrate. What happened to the lady before me doesn't happen very often, but it's not unheard of.
With my first he was born exactly according to my menstrual cycle date. Which was 5 days earlier than the doctors due date
I am every time I go to the doctor she asks for the day of my last menstrual cycle like as if the date going to be different from what I've been told