Abdominal ultrasound behind vaginal ultrasound measurements?

Katie

So just curious if anyone has been through this... I went to my fertility doctor on Friday was measuring 9 weeks 1 day( a day ahead). Yesterday I measured 9 weeks 5 days on an abdominal ultrasound at my OB. The sonographer did a 30 second ultrasound and did not recheck the measurement when I asked her since I thought it was behind. Should I be super concerned? Is it just the difference in the type of sonograms?