Baby Hints & Tips

LMP or Ultrasound More Accurate

Expected date of delivery (EDD) is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). Ultrasound of the foetus at 6 to 7 weeks can also be used to measure the foetal size to confirm the expected date of delivery. 

Community question

Just wanting to know if any others have had an EDD from a scan that was different to the EDD calculated based on their LMP (last menstrual period). Which was correct in the end – the LMP due date or the estimated date of the scan?

LMP or Ultrasound More AccurateSee abbreviations explained here

Scan date was more accurate for estimating my expected date of delivery

  • I was given two dates. The hospital staff all went off the scan date & going by the scan date I gave birth at 40+1 Vicky
  • I was given three dates. The first was the 23rd, then it got moved to the 25th. The 20 week scan said I was due on the 20th and she arrived on the 18th. So it just goes to show you babies come when they are ready and not when we think they should come April
  • My edd from lmp was jan 16 and edd from the scan was jan 24th. Bubs ended up being born jan 27 so the scan was right i suppose Dani
  • My second I was positive I’d ovulated really late, about 10 days past when I ‘should’ have. This matched with the first blood tests I had to confirm pregnancy and was confirmed when I had the first US at 12 weeks. As I was planning a vbac I made sure the Dr went by the scan date, not lmp. LMP would’ve put me 10days further along which is a big deal at the end of pregnancy when so many drs start talking induction!! Karlie
  • The dating scan is most accurate as the earlier the scan the more spot on it is. You can tell them your LMP but you may have not ovulated when you thought you did. I was certain that I was 6 weeks (ovulation day 17) but turns out I was 6+4 and ovulated on day 13. I’m now 37+2 and has been accurate. So go by the scans Tamsyn
  • Either way it’s highly unlikely a baby would arrive on its due date. Ask your Dr which date they’re going by. Natalie
  • Yes and their date was correct. Early stages like 6-12 weeks most babies are the same size so I wouldn’t argue with it. Go by their date and wait and see if you were right. Stacie
  • Yes I was given a date 7 days different and my first scan and then a date 3 days different at my next scan and then at my 12 week scan I was told the correct date exact on LMP and then I was asked later if my dating was wrong because he was smaller than he should have been which ended because I had pre eclampsia Alecia
  • My LMP said I was due on Nov 4, my EDD by scan said the Nov 12. My Midwife said they would only let me go a week over as they weren’t sure. I ended up being induced on Oct 21, and bub arrived on Oct 22. Hayleigh

Last menstrual period was more accurate

  • My due date for LMP was 1/1/15 and my scan was 28/12/14. She was born on 3/1/15 Jasmine
  • I calculated my due date at 30.06.2014 and then when for my first scan and they said no the 7th of July and then got told no the 3rd of July but the 30th of June was correct so LMP Amy
  • Based on last menstrual period I was due 28/12/14. Scan said 7/1/15. I had my daughter on 1/1/15 so in the middle Heather
  • My baby was always measuring large. She ended up coming 2 days after due date calculated by lmp Emma

Nothing accurately predicted baby’s arrival

  • I was given 2 dates one at 8 weeks at a dating scan and one at my anatomy scan at 12 weeks both were wrong she ended up coming 5 days early. Babies come when they are ready hence “expected due date” Jessica
  • My EDD and LMP dates were different I also knew exactly when we conceived and that due date was different as well. In the end they were all wrong. Babies come when they are ready…. Even if the wait does drive you around the bend Kira
  • My scan dates and LMP dates where about 4 days different from each other.. In the end she didn’t come on either, made me wait. When someone asked my due date I would say ‘end of october/early november’ that way I was covered lol Nikki
  • Neither method is 100% accurate. And the baby decides when they are coming. My tip is to have a bag ready to go nice and early, as our boy was 3weeks early Ben

Was your LMP or ultrasound more accurate, comment below

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  1. Avataramanda says:

    I’m going through this now
    My lmp was 18/12/14 making my due date 24/9/15,
    My scans from day one say 19/9/15 which I know is more accurate as I know I ovulated early,

    I’m sticking to my dates only time will tell

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