Still confused

[bigcat21]

My partner  had a vaginal ultrasound done and the physician did a crown rump measurement. The machine calculated her to be 12wks 6 days. What does this mean? Is that the time she concieved or is that the date of her last menstrual cycle?

[bigcat21]

Thank you for your comment, it cleared things up for me! Have a great week!

[jessbbg]

Yes, that gives you approximate date of last menstrual period based on the baby's stage of recognizable development.  

The flaws with this can be that some women may have had delayed ovulation (everyone is different and cycles vary), plus the "journey" of the ovum can take anywhere from 4 to 15 days to get to the uterus (and sperm can live a number of days), so it's a general idea, and is not meant to be a definitive date.  

If you subtract 14 days from the age they give you at ultrasound, that is their best guess at the date conception took place.  This can give you a little bit better idea, but is still imprecise (sperm living for days, etc).  Interestingly enough in studies where the date of conception is known (fertility treatment studies involving multiple women, etc), there is still easily a week's variation in visible development at various times.  

Hope that helps give you a better idea/understanding.  

[worriedbabe]

that's the date of her last menstrual period, that's when pregnancy is measured from.