Preg.sonograms done on my 8th wk. preg. says my duedate is 17/18th of sept.2013.unprotected sex on the 15, 17, 22 &26 dec.'12.when did i conceive?

December 24 or 25: If you subtract 9 months and 1 week you get the probable date of your last period. Add two weeks to get conception estimate. Ultrasound is good within about 5 days if done vaginally at 8 weeks. So you could make almost any of those dates work.

12/22or26: We don t know what day you had the ultrasound but can use the estimated due date to calculate your conception date. One conceive roughly 2 weeks after you first day of your last menstrual period. This would roughly be december 10 with conception on or around the 24th.