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Thread: What is more accurate? Date of conception or dating ultrasound?

  1. #1

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    Talking What is more accurate? Date of conception or dating ultrasound?

    Hi all



    So I am pregnant again and over the moon, but it came as a bit of a surprise so I am not sure of when my LMP was. Since we already have 2 little sprockets our alone time is few and far between so I know the exact date of conception, however the date's of conception do not equal the date's of the dating ultrasound. Basically it's only a couple of days' difference, but when you have a history of babies that come 2 week's early and still weigh over 10lb a few day's of extra growing is a BIG difference!!!

    If I go by the ultrasound date's I am only 8 week's today, but by my conception date's I am 9 week's on Sat. What are the chances of the dating scan being wrong? I know it's only a few days, but I want to know for sure.

    thanks for reading my long question

  2. #2

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    I'd go by the date you are sure you conceived. My dating scan put me behind by about 6 days which I knew was impossible as we only DTD once that whole cycle and i got a feint positive very early. if I conceived when the dating scan said I did I would have got a positive HPT at like 5 or 6 DPO which would have been extremely unlikely. My GP swore the early dating scan was correct, but I knew better. And sure enough when I had my 12 week scan bub was measuring as per "My" dates.
    Go with your gut feeling for sure

  3. #3

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    It can take up to 24 hours for 'conception' to occur from memory, it isn't an instant thing So if it is only a day or so out, then I would think they are actually the same, iykwim.

    Take the middle ground but either way, it isn't much difference.

  4. #4

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    Both my ultrasounds were out by 10-12 days (saying i was due later than i thought with my dates). DD1 came a month before my date and six weeks before my u/s date but she definitely wasn't six weeks early. Dd2 came right on MY due date, 10 days before my u/s due date. I'd be putting faith in your due date seeing as you were so sure of conception

  5. #5

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    Your own menstrual cycle, always. Machines are based on averages and mathematics. We all have unique cycles hence why we never give birth on the guess date either.
    Kelly xx

    Creator of BellyBelly.com.au, doula, writer and mother of three amazing children

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  6. #6

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    Yep, I would go with your conception date. I totally understand where you are coming from though....my DS was 11lbs 2 oz, although he was two weeks late (going by my conception dates).

  7. #7

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    DTD date isn't always the same as O date though. Do you know when you O'ed cos that could be the 5 days difference IYKWIM?

  8. #8

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    I would say U/S due date since ovulation day and BD day are not necessarily the same. When I was PG with DS my LMP due date was 6 days before my U/S due date and he was born on his U/S due date.

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