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Question about accuracy of dating based on early u/s

Julie822Julie822
in October 2011 Moms
Does anyone know how accurate dating is based on early u/s? How many days +/- your expected due date is considered "normal"? I had an u/s last week and this week - last week was showing I was 6w4d when I expected to be 6w5d and today's said 7w3d when I expected to be 7w5d. The doctor didn't seem concerned about this so I am not either - I was just wondering what others experiences have been.
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Re: Question about accuracy of dating based on early u/s

  • CheesyPeasCheesyPeas member

    I think there's certainly some wiggle room in there.  At my u/s today, the ultrasound tech told me that they don't adjust due dates unless your measurements are more than a week off.  She said you can lose and gain a few days throughout.

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  • LisaMarie_LisaMarie_
    I've always just gone by my due date and that's that. When I went in for my ultrasound I was 6 weeks 4 days and the tech said "oh ya you are 6 weeks" and he even labelled my ultrasound pictures as 6 weeks 0 days.. which would make no sense based on the first day of my last period.
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  • SpinningJessSpinningJess
    I read last night that u/s dating can be +/- 7 days.  I wouldn't worry about a couple days whatsoever!
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  • cantalopes24cantalopes24 member
    imageLisaMarie_:
    I've always just gone by my due date and that's that. When I went in for my ultrasound I was 6 weeks 4 days and the tech said "oh ya you are 6 weeks" and he even labelled my ultrasound pictures as 6 weeks 0 days.. which would make no sense based on the first day of my last period.
    Unless you were charting there is no way to know exactly when you ovulated, and even that is occasionally wrong. With my son they changed my due date twice but I got pregnant months after my last period because of irregular cycles and was 8 weekish when I found out so dating was hard to do.
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  • Runnergirl2242Runnergirl2242 member
    I have been about three days back and forth. I have had three ultras, its always been a little behind my expected gestation but it varys back and forth a few days. It is nothing to worry about.
    DS Born 10/05/99 DSS Born 7/11/95 BFP 05/11/10 - Missed M/C, D&C 06/23/10 BFP 8/3/2010 - Ectopic, Methotrexate 8/17/10 BFP 1/27/11- Please God let this heart beat strong. Beta1 17dpo-314 Beta2 20dpo-883 Beta3 22dpo-1861 Beta4 25dpo-5918 DS2 Born 10/07/99 "I prayed for this child, and the LORD has granted me what I asked of him. So now I give him to the LORD. For his whole life he shall be given over to the LORD." 1Sam1v24to28.
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  • PinkLadyRN1PinkLadyRN1
    Usually the ultrasound machine calculates your gestational age based on the babys crown to rump length.  It's usually more accurate than the wheels they use in the office.  Since those are based off a regular 28 day cycle!
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  • LisaMarie_LisaMarie_
    Of course.. I didn't say my method was for everyone.. lol I've been charting for the past 3-4 years so that's why I said that. And I've always had regular cycles.
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  • LisaMarie_LisaMarie_
    Shoot I always forget to quote! lol
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  • fraglettefraglette
    I know, when I ovulated (charting) and showed it to my NP, but I think she's sticking with my LMP because she said I'm measuring at 6,3 which is based off my LMP. It's a 3 day difference, so I'm not going to worry about it. We're hoping I'll be late anyway.
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  • KaraG2BKaraG2B
    The accuracy of ultrasound for dating purposes is fairly accurate in the 1st trimester, +/- 3-5 days. (This 3-5 day discrepency is why they will usually stick with your LMP if you're within a week or so). As the pregnancy progresses, it is not as accurate.
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  • Ritzy19Ritzy19 member
    It actually says on my ultrasound picture  +/- 2 days after the date, so I really wouldn't worry about it.

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  • Lambie.Lambie. member
    imageKaraG2B:
    The accuracy of ultrasound for dating purposes is fairly accurate in the 1st trimester, +/- 3-5 days. (This 3-5 day discrepency is why they will usually stick with your LMP if you're within a week or so). As the pregnancy progresses, it is not as accurate.
    This. And of course it varries by the picture that is taken. That being said, That is a narrow window and very accurate. Much more so than later in pregnancy.
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  • Lambie.Lambie. member
    imageKaraG2B:
    The accuracy of ultrasound for dating purposes is fairly accurate in the 1st trimester, +/- 3-5 days. (This 3-5 day discrepency is why they will usually stick with your LMP if you're within a week or so). As the pregnancy progresses, it is not as accurate.
    This. And of course it varries by the picture that is taken. That being said, That is a narrow window and very accurate. Much more so than later in pregnancy.
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  • ally510ally510 member

    I had my first u/s today.  Based on the date of last period (1/15), I should have been 6 weeks, 3 days.  However, I was using ovulation sticks, so I knew I ovulated 5 days late.  Sure enough when they measured today, my little one (very little one) measured 5 weeks, 5 days.  Spot on from the day I knew I ovulated, so I think they're fairly accurate.  That said, I think it also depends on the skills of the technician.

    While I'm super early, I was thrilled because we got to see a heartbeat!!! 

     

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  • liebhard2liebhard2 member
    the earlier you are the less accurate your dating will be just because theyre so small and hard to measure.  Last friday I went from 7weeks 3 days to this monday being 8 weeks 2 days.  Doc said that that's why alot of women don't have US to date until 8/9 weeks because the baby is more accurate to measure
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  • Julie822Julie822
    Thanks everyone - I guess it is pretty amazing that they are as accurate as they are, even with a few days error!
    EDD - October 13, 2011 - Can't wait to meet our little one! BFP cycle BabyFruit Ticker pregnancy calendar
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