Based on my last period my due date would be December 20 but all the ultrasounds I had don't match with the date, the first one that I had at 6 weeks showed due date on December 24, at 9 weeks December 26. Now I'm 21 weeks and had an ultrasound few days ago showing due date on December 23. My Doctor never changed my due date And I know I shouldn't trust the second trimester dating but I was off few days since the very beginning. What you think? What's your experience?