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are 12 week scans accurate? if you know when you concevied was your scan accurate?

laura1991hghlaura1991hgh
in 3rd Trimester

I went for a scan at 12 weeks which they measured the CRL at 12 weeks 2 days. But I think it mite have been 4 weeks out and I was actually 16 weeks. Is it possible to be out by this much? I am now 36 weeks pregnant (according to scan date) and am concerned I mite actually be 40 weeks pregnant? And now the doctors may let me go 4 weeks over due! Has this happened to anyone before or is being pregnant for 44 weeks not possible? 

 Also if anyone knows when they conceived was your 12 week scan accurate?

 I know have just posted this on 1st trimester board, but as someone pointed out many of them have not had 12 weeks scans yet! 

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Re: are 12 week scans accurate? if you know when you concevied was your scan accurate?

  • hollyg1920hollyg1920 member

    i also responded on 1st tri...

    Are you saying that you had an u/s at 12 weeks and the baby measured 12w2d but you think you were 16 weeks pregnant?  Just trying to make sure I am not confused.

    12 week scans tend to be pretty accurate, although some babies might start to measure bigger or smaller within 5 days of EDD.

    What makes you think you might be 4 weeks farther than your doctor thinks.  If you are basing it on LMP do not go by that, not everyone ovulates 14 days after the start of their period.  It is very possible you ovulated very late in a long cycle.

    I would say if your baby measured 12w2d at the 12 week scan then you are really 36 weeks and not 40
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  • silvercamaro77silvercamaro77 member
    I agree with other people.  Especially since if you're due date were truly off by 4 weeks, at some point during the pregnancy LO would have measured off.  If LO were measuring an entire month larger, they would want to induce you before you hit the 40 week mark.

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  • sdo_082989sdo_082989 member
    Mine was actually dead on. I was keeping track of ovulation and taking ovulation tests. Well my EDD based off my LMP was 12-5-11. When I went for my 12 week u/s the baby measured behind and they put my EDD as 12-17-11 and that date was EXACTLY 40 weeks from my ovulation (not saying I was dead on but sure we were close). I had DD on 12-21-11 so I was a little OD but I say they are within a week accurate. 

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  • acaudill75acaudill75 member
    The earlier scans are usually the more accurate ones, since there are a lot more growth milestones specific to gestational age (like organs showing up consistently with every baby at certain specific times). Even though I had no idea I was pregnant this time around, I guessed at my LMP and conception date, and was only off by one day. But, I have had a regular period without birth control all my life. I am definitely not the norm. With all due respect to you, you probably didn't ovulate when you thought you did, and you are indeed only 36 weeks pregnant. I don't know what the Guiness World Record for longest human gestation is, but its pretty rare to go past 42 weeks. You will give birth when the baby decides its been in there long enough.
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  • Ashley&ScottAshley&Scott
    They would know if you were measuring ahead at 36 weeks. If the doctor had any concern about this they would send you for another ultrasound.
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  • J&JSuiter070205J&JSuiter070205 member
    The earlier the scan, the more accurate it is. So yes, a 12 week scan should be very accurate (unless something is wrong with the baby's developement).  My ultrasounds have always been within 2 days of my due date based on my LMP.
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  • salt78salt78 member

    I know when I conceived and my 12 week scan was exactly accurate.

    Were you tracking your ovulation when you got pregnant? You may have ovulated later than you think and your LMP date would mean nothing. If I went by my LMP date, I would be several weeks ahead of where I am now too because I am a late ovulator.

    It is highly unlikely that you would be measuring 4 weeks behind at your scan. 

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  • greeneyed_bridegreeneyed_bride member
    I was charting, so I know the exact day I ovulated. My ultrasound measurements at 6 weeks and 13 weeks were only off by like a day. I seriously doubt that you measured four weeks behind at your twelve week scan. What makes you think you're four weeks farther along?
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  • futuremrsbutterflyfuturemrsbutterfly
    imagelaura1991hgh:

    I went for a scan at 12 weeks which they measured the CRL at 12 weeks 2 days. But I think it mite have been 4 weeks out and I was actually 16 weeks. Is it possible to be out by this much? I am now 36 weeks pregnant (according to scan date) and am concerned I mite actually be 40 weeks pregnant? And now the doctors may let me go 4 weeks over due! Has this happened to anyone before or is being pregnant for 44 weeks not possible? 

     Also if anyone knows when they conceived was your 12 week scan accurate?

     I know have just posted this on 1st trimester board, but as someone pointed out many of them have not had 12 weeks scans yet! 

     

    I know exactly when I conceived (minor OCD lol)---Our 12 week scan was pretty accurate and only off by a few days (12 week 3 days)--not enough to change our due date.

    What makes you think you are 4 weeks off?

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  • laura1991hghlaura1991hgh
    thanks for all the replys, I only think I mite be 4 weeks out as the conception date they have given at the scan I did not have unprotected intercourse and only did 4 weeks prior to that date! maybe the protection I used didn't work and I am actually 36 weeks. as everyones elses dating scans seem very accurate.. I was going along with the scan dates, but everyone says how big I am for 36 weeks and in comparison to others at my baby group who are as far a long as I am, I am huge! iv also been engaged since 33 weeks which I thought was very early? thanks for replys though feeling a bit less worried that scan date is wrong now!
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  • Ivana_StolichnayaIvana_Stolichnaya member

    That's a big time difference.  I was charting and know exactly when I conceived from the O date.  My Dr.'s office measured LO at 3 days sooner.  I had March 8th as my EDD, Dr. has me at March 5th.

    Last time with my Daughter I had it put down to Oct. 15th, Dr. had me at Oct. 12th.  I went into labor on the 12th and she was born on the 13th.

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  • NiniJ55NiniJ55 member

    I knew exactly when we conceived since we did fertility treatments and I was very closely monitered.

    My scan that was performed right around 12 weeks was off by a few days and as a result my due date was moved up a little.  Same exact thing happend when I was pregnant with my son - we knew conception due to fertility treatments but the scan was a little off.

    I think it would be a little outrageous for the scan to be off by 4 full weeks, though.  And you were not measuring differently during your other scans??  The 12 week scan is pretty accurate.

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