Accuracy of Early Ultrasound Scan


Hello! I Was hoping for your opinion regarding ultrasound and conception dates. Is it at all possible that my first ultrasound indicating 8weeks 5days on November 3rd and a second ultrasound on November 29th indicating 12weeks5days could in any way be corresponding with conception on or after October 1st?

My periods are irregular, so I'd feel better scientifically going through the possibilities.

Thank you!


If you had an ultrasound on November 3rd showing you were 8w 3d the estimated conception date would be approximately September 17th.

If you had an ultrasound on November 29th showing you were 12w 5d the estimated conception date would be approximately September 16th.

Both of your ultrasounds show the same results. The error ratio is not more than a week this early in pregnancy. This means an ultrasound is quite accurate in the first trimester. I would think you most probably conceived well before October 1st.

Please note that a paternity test is the only way to tell for sure. If you are always going to wonder, please go ahead and do the paternity test for your own piece of mind.

With regards,
Jane Foley RDMS

Jane Foley

Jane Foley has worked as a Sonographer (Ultrasound Technologist) since 1979. Jane has lived and worked in many parts of the world including Saudi Arabia. She is a Registered Diagnostic Medical Sonographer or RDMS. She pulls a wealth of information from her experience in the field of Radiology and her interactions with such a broad cross-section of cultures she has visited. She now makes her home on the island of Maui with her English husband, Michael.