ultrasound accuracy

[yessicah]

i had an ultrasound october 15 2007 and said my crl was 7 weeks i dont know exactly if i give the right lmp date which i think it was 8/24/2007 they put that date when they did the ultrasound, would the ultrasound tell me if i am more than 7 weeks pregnant  or are they doing it from LMP

[Keith Downing, MD]

Hello,

Good question.  It is not uncommon for pregnancy dating by ultrasound (U/S) to differ from dating determined by the last menstrual period (LMP).  The earlier the u/s the more accurate it is in determining the age of the pregnancy.  U/S is often used to confirm a woman's dating and if there is a discrepancy, the u/s dating is used.  General guidelines are that if a 1st trimester u/s differs 7 days or more, or a 2nd trimester u/s differs 14 days or more from the due date based on the LMP, the u/s dating is used.  If the due date is within the 7 or 14 day window the LMP is used

Also, if a woman is not certain about her LMP it is usually best to use u/s dating.  Given your LMP is uncertain, you should base your dating on the 7 week ultrasound.

Best regards,

Dr. Downing

[Ally26]

The ultrasound would give you accurate dates they just use the LMP as a guideline.. So if it said you are measuring 7 weeks then thats what you would be.. it is all a bit confusing i know.. I have been doing a degree on sonography ultrasound and still find things confusing at times i am 15 weeks at the moment and am suppose to be by LMP 17 weeks ultrasound picked up i am 2 weeks behind witch is normal because all my other babies were the same.. good luck with everything hope this helps

[beatrice352]

The ultrasound has become so helpful now refer to the time before it was used routinely as "the olden days." We use it to diagnose twins early on; we use it to document appropriate growth as the pregnancy progresses; we use it to determine fetal health; Of all of these uses, dating the pregnancy is the most common reason to use ultrasound, particularly when the expectant mother cannot remember the date of her last period (as in breast-feeding or irregular cycles). Even when the last period is known, ultrasound is reassuring to demonstrate adequate growth, especially when there's a risk of delayed growth, as in hypertension or smoking, or if there's the risk of exaggerated growth, as in gestational diabetes. It is not uncommon for babies that are labeled "Large for Gestational Age (LGA)" and "IntraUterine Growth Restriction (IUGR)" to have monthly or even weekly ultrasounds during the pregnancy.