2 weeks Difference!!!!

[Amaras Mommy413]

I'm pregnant with my second child. There is only a 8 or 9 day period that I could have gotten pregnant as my fiance was only in town from July 28-Aug 7. If rumors are true that sperm stays viable for 5 days, that would make due at the latest May 5th. When I did my confirmation ultrasound at 13 weeks, they put me due May 17th, then at the regular 20 week ultrasound, changed it to May 24th. Is it possible for these 2 ultrsounds to be off by more than 2 weeks?

[CEG]

Ultrasounds done at 20 weeks pregnant are considered only +/- 2 weeks accurate.  so it would not be unexpected for the due date to be two weeks diffferent.

It is considered poor practice to change due dates based on a 20 week ultrasound unless there are no other reliable methods of dating because of the accuracy problem.  So if you have a 13 week ultrasound the date should be taken from that one.