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Thread: Dating scans

  1. #1

    Default Dating scans

    Hey there,

    Does anyone know which scans are more accurate.

    I had a very irregular cycles, no period for 4 months, then one in 2 months, so I had no idea on dates.

    My first scan was done at 4w5d then another at 5w6d (first ectopic check, second viability), then another at what I thought was 9w3d but it showed me at 9w6d.

    Because I'm trying to get the timing right to get an NT scan, does anyone know if the earlier or the later scan would be more accurate for dates? The very first only saw a sac and measured that, the second saw a tiny seed with a HB and measured the seed, the third measured a very obvious baby.

    Just unsure...according to the last scan I've booked my NT scan for 12w3d, but I'm concerned that if the earlier scan was more accurate that I'll be only just on 12w for it...maybe too soon.

  2. #2
    Percy Guest


    I would go for the later one as the earlier ones tend to be more ball park figures then accruate ones.

    FYI I had my 12 week scan at 11w6d and they could see everythign fine do I wouldn't worry about being a few days out.

  3. #3

    Join Date
    Oct 2003
    Forestville NSW


    Actually Percy I've heard its the other way around... that the earlier scans have more accurate dating. With this pregnancy my first scan gave my EDD at 28th of October & my second scan gave my EDD at the 15th. Well... still cooking away in here ... As for NT testing I was concerned as well but they said anywhere within a week to 10 days should be okay... 1-2 days won't make much difference.

  4. #4

    Join Date
    Oct 2006


    Hi Tara

    I'm not sure the answer to your question but I have booked in for my NT scan when I will be 12w 1d and my doctor said that was fine. I don't think being a few days out would make any difference.

    I' m due around the same time as you! How exciting....! Enjoy your next scan!

  5. #5

    Join Date
    Aug 2006


    Hi Tara.

    You can have your NT scan anytime from 11 - 13 weeks so you will be fine! My dates have also changed each time I've had a scan, with my EDD coming forward each time. The earliest scan should be the most accurate and then your dates are adjusted according to hos your baby grows. If it is growing well, then your dates might come forward and your EDD will be earlier. Remember that they are estimates anyway and almost no babies arrive on their due date!

  6. #6

    Join Date
    May 2004


    A few days makes no difference for the NT and the u/s measurements are always +/- 7 days at any rate.
    Good luck for your scan!

  7. #7


    Thanks so much for the replies.

    I can't begin to say how great it's been to have a forum to post on and get answers. I live in a place where it's an hour and a half away from hospitals, etc, and it's not easy to get into seeing doctors. Before last week, I hadn't even heard of an NT scan and I had no idea what time I was supposed to book it in. One post on here and I get all these answers and know what I'm doing when I rang up to make the appointment.

    I should have done more research on it as well, but because I've had such a big threat the whole time of losing the baby, I havent thought ahead at was too hurtful and scary to do so and too upsetting to read about the next trimester. So I had no idea about this scan.

    Thanks so much for your answers. I have been told in last pregnancies that the scans were more accurate done earlier, but it didn't really matter to me then the EDD or the time because they never offered or had any of these scans last time (not that I was told about anyway) so the actual dates didn't matter too much. Only 5% of babies arrive on their EDD! Then this time i find I've got a week and half leverage to get the NT scan done and you can't do it too early or too late.

    It's been very confusing but it's great to be able to ask questions on here. Thankyou so much again.

  8. #8

    Join Date
    Jan 2005


    I was told the earlier scans are more accurate, because as you get further along there is a lot more variation in babies' size etc (i.e. not all full term babies are the same height/weight etc)

    It was tru for me anyway. My first scan only dated me 10 days earlier than milo was born, where was my scan at 35 weeks dated him at a month before he was born *LOL*

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