If ultrasound shows due date of october 31 what was the earliest and lastest date i could have gotten pregnant. ultrasound done in july 2014?

Due date: This depends, was the Ultrasound done during the first trimester? Do you know you last menstrual period (LMP) - because if you are certain about this and it coincides with your dating by ultrasound you can be be assured the due date is pretty accurate. A 1st trimester U/S used for giving a due date is pretty accurate by itself as well. Answer: February 7 plus or minus a few days was conception.