Can ultrasounds lie about how far along you are? also if your ultrasound says your 9 weeks, did you get pregnant from sex 9 weeks ago?

9 weeks pregnant: Since women usually know the date of their last period, at least more likely than the date they conceived, doctors have long used the menstrual period as our landmark for when the person concieved. You usually conceive about 2 weeks after the last menstrual period. So, confusingly enough, "9 weeks pregnant" means you actually conceived 7 weeks ago! ultrasound is accurate give or take a week.