confused about gestational age

[xxxxxsamxxxxx]

I am pregnant and had my last period on the 7th of september, but my periods recently became irregular after being so regular for so long. working it out from my last period i should be about 7 weeks and 4 days pregnant, but after having a scan today i was told i was only 6 weeks and 3 days pregnant. How accurate is a dating scan? So confused!  

[NewAFwife]

Ultrasounds (especially that early) are the best way to date a pregnancy.  If your periods are irregular, then you could have been off by a week or so as to when your ovulation was.  Also, if you do not have a 28 day cycle, than typical dating methods will not work, and you O later or earlier than those with a regular cycle.  The ultrasound date is probably right, since they go by size and stage of fetal development, so trust that.  But keep in mind, your due date will probably change a lot, so this time it is not set in stone!

[mamaofonetrying42]

u/s scan is the date to go by. It is the accurate date you can get.