Dating scan — The Bump
2nd Trimester

Dating scan

Now which is the official dating scan, the 12 week one or the 20th week one?
My dr got so angry and upset that I missed my 12th week scan and she said without that my sure date cannot be accurate made (sure dates are an estimation no matter what they are isn't it?) But the thing is with my last pregnancy my dr who I have birth to changed my due date by a week before depending on the 20th week ultrasound, then why on earth does this women make life miserable for me. (I am high risk after 3 losses) but I don't think so a 12 week scan can do anything on those regards.

12 or 20 which one does your dr prefer?

Re: Dating scan

  • The most accurate dating scan will be in the 8-12 week range. By the time you have your 20 week scan, it's too late to use it to date the pregnancy, but you may learn at that point the baby is measuring behind or ahead of the expected date, and that could be important information. 

    However, lots of people don't have an early dating scan. They just use the date of your last period to find your due date.
  • Those scans are looking at different things that can only be seen at those times, no necessarily dates. The 12w US is looking at nuchal translucency among other markers which can indicate certain genetic abnormalities and indicate that more invasive tests may be needed. The 20w scan is the anatomy scan that looks at all of the structures of the fetus in great detail to check for anomalies. 
    run along Pond...2015/12/10

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  • The earlier an ultrasound is done the more accurate it is for dating. This is because early embryos/fetuses grow at a more predictable rate and at a certain point the babies normal growth starts and some babies are bigger than others. However if you can't reschedule your 12-week then it's kind of a moot point... you already missed it right? Many women don't have dating ultrasounds, go by LMP, and baby comes when baby's ready. 
  • I would go to all the early u/s if they're recommended by the OB. It helps to see the LO and make sure growth is on track and everything is looking perfect! We opted out of chromosomal/genetic blood tests so I rely on the u/s to tell me all is well. Take care!
    Me: 30 DH: 32
    BFP#1: 9/9/2014 DS born 4/7/15
    BFP#2: 6/16/2016 MC/D&C: 7/29/2016
    BFP#3: 10/14/2016 (fingers crossed for a sticky bean)
  • My dating scan was early because of irregular cycles. At the time it turned out at 7+3 
    So my EDD was 6/11 
    My 12 w scan proved +2days with a dd of 4 /11 but they stuck with the 6th
    My LMP date was two days different .
    At my midwife booking in appt yesterday she changed it back to the LMP based on my previous cycle being "normal" telling me it's only 2 days and they go with the later date so thats 2 extra days before they count the 2 weeks after 40weeks before inducing so if I go over I have those two days longer be for that count starts for baby to come naturally .  
    She said usually they switch to the scan date if the difference is more than 5 days otherwise they give you the latest so I went from 13w to 12w+5 on the spot and my new EDD is 8/11 

    I imagine for you being High risk they just want as much information as they can to monitor but will go by your LMP date and compare that to the 20w scan .
  • MyNamesTakenMyNamesTaken member
    edited May 2017
    Where I am the scans you get are:
    Dating US - between 6-7 weeks to verify pregnancy and set due date
    IPS US - around 12-13 weeks to test for nuchal tube defects and other issues (combined with blood tests)
    Anatomy US - around 20 weeks to check development of all organs, limbs, etc.

    Each scan has its own important purpose and the earlier the scan, the more accurate it is in terms of calculating your due date. I would think if your doctor specifically ordered a test for you, it's not unexpected that you missing it upset her, especially if you're high risk. They may compare the 12 week to the 20 week to come up with something, but I don't know.
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  • She didn't specifically book any thing for me, infact I went to another dr before her.
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