Ultrasound Determining Conception

Jane Foley's picture


Dear Ms. Ultrasound,
I found out I was pregnant on Dec 1 of 2008. I had an ultrasound performed on Dec 11. I was told then, that I was 8 weeks and 2 days pregnant. A heartbeat was revealed that day as was the yolk.

I'm curious how close the u/s can actually determine the conception date. How closely the scan can determine the age of the baby. I understand the calculation by using the date of the last period, but I could guess at that without the u/s.

If the u/s states I'm 8 weeks and 2 days on Dec 11, is it possible it could be off enough to allow conception to have been on or after Nov 2nd?

Thanks for any help. I have a photo from the u/s, if needed.


Hello, From your ultrasound on Dec 11th. If you were 8 wks 2 days, conception would have been close to Oct 27th. These early ultrasounds are usually fairly accurate. They can be 3-4 days off one way or another. In your case this is only 6 days from your Nov 2nd possibility. I would say this is too close for comfort and a paternity test would be necessary if this is your concern.

With regards,
-- Jane RDMS