Discrepancy in Fetal Age

Jane Foley's picture

QUESTION

Dear Ms Ultrasound,
Yesterday I had an ultrasound at 8 weeks pregnant (from my LMP). The doctor said everything looked good with a fetus and a heart beat but said ultrasound showed I was only 6 weeks 3 days pregnant.

How can this be? I know I ovulated on the 14th day and had intercourse up to and including that day, but not after that until after my pregnancy test came back positive. Should I be concerned?

ANSWER

From the dates you gave me from the ultrasound, you should have gotten pregnant around December 20th. Counting days and trying to figure out the moment of ovulation is not an exact science. We never know the exact moment of conception.

Do not worry! A discrepancy such as this must take other factors into consideration, like the statistics the doctor's machine has programmed into it, to where he chose to place the calipers that measure the fetal pole. He may have measured it at 6 wks 3 days and I could come in and say 7 wks.

It's all very operator dependent. It sounds as if the doctor saw a normal fetal pole and heartbeat. This should stop you from worrying.

-- Jane, RDMS