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Scan dates make no sense??

Ok Ladies, Get ready for the Maths... image

I used the calculator below but have also tried many others online giving same dates.

My LMP: 18th November 2009

Due: 25th August 2010

Conception: 2nd December (roughly based on 14 days past LMP date)


However based on size of flump, my scan yesterday says Baby is actually due on 5th September 2010

This dates conception as 13th December 2009 which is impossible!!

I have 27 day cycles and AF was due on 15th December, we got our BFP on 16th December.

Implantation occurs about 6-10 days post ovulation and would be implanted for about 48 hours minimum before you found hCG in urine.

Are you still with me?? :lol:

Well... to have a BFP on 16th December, it means that the latest our flump could have implanted was 14th Dec. That also means that if flump was conceived at least 6 days earlier (8th December) which is again earliest implantation scenario. It gives a EDD of 31st August 2010?? It wouldn't be possible to be dated later than that and have a BFP on 16th?

Makes no sense to me?? So from my LMP, I should be exactly 8 weeks pregnant today, but they are saying I'm 6 +3

No Way!?


  • I think it's normally quite difficult to 'date' you from an early scan?

    I would not worry too much - go with the dates you have worked out (you know your body better than anyone else!) and see what they say when you are scanned at 12 weeks...

    All the dates I was given were wrong up until my 12 week scan - which gave my EDD as one day before the date I had calculated myself!

    Cath x
  • Hello

    It is confusing the way the medical world decide to date us, but its to keep the whole thing uniform.

    Firstly forget conception dates, its totally irrelevant in how they work out your date.

    Secondly scans are based on the average- so the size your baby is in the scan is measured against the average size at every week and they work out roughly your due date from that. Sometimes it sets you ahead, sometimes it sets you behind.

    You can ask, if it makes it easier for them to simply take the date of your last period as the date from which to calculate your due date. Thats what I have done. They are not always keen to do that, but that put me slightly behind my scan date and so gives me longer before they would induce.

    I would not worry too much about dates, only 5% arrive on their due date, and your 20 week scan will probably give you a clearer idea of when that might be.

  • hello

    early scan are not always accurate which is why the dating scan is at roughly 12 weeks,

    there has been a lot of ladies recently that have worried at an early scan to find at the 12 week one baby has caught up or even overtaken the dates they thought.

    are you getting another scan? i would personally stick with your original dates until your 12 week scan x

    becca x
  • I agree with **Cath** it is very difficult to give you accurate dating so early on, I went for a scan at 9 weeks due to bleeding yet they dated me at 8 weeks, when I went for my proper dating scan, from my dates I should've been 13 +3 and I measured 13 weeks so almost back to normal!
    Try not to worry about it,, all will be revealed at your next scan I am sure!
    Clare x
  • Sorry to gatecrash, but does that mean they often re-date you at your 20 week scan? I was dated as 10+2 at my first scan and I had been convinced this was a week out based on LMP and the date I had thought we conceived, but I have my 20 week scan in a fortnight and wonder if it will be 'corrected'???
  • HI g/c from baby

    definately agree thats dates from early scans are not accurate, just half a milimetre at such an early stage can change ur date by a week. ur 12 weeks scan will be far more accurate. i fell over at '7' weeks by lmp (edd 18th march) and was sent for an early scan, the sonographer then said that i was only about 4.5 weeks (edd 2nd aprl), then at 12week scan i got edd of 15th march, so that early scan was completely out, and from then on he was smack bang on avaerage size for babies edd on 15th march, iyswim? and my 20 week and 28 week scans both also gave the same edd if 15th, so i wldn't take an early scan as red, as its not ur offical dating scan anyway, wait for ur 12week scan and that'll give u a much better picture of how far along u are. they won't change ur dates anymore after its been done at the 12week scan, if baby ends up being too small or too big at subsequent scans compared to edd givin at 12weeks then its usually an indication of growth problems (but only if its more than 2 weeks either way) hth xx
  • emsyj the 12 week scan is the most accurate, babies grow at a very predictable rate between 10 and 13 week roughly so they can date you accurately from your 12 week scan and in most circumstances will stick with this date no matter what any future scans say.

    Having said that my date has been changed late on and like you Fairythalia it makes absolutely no sense.

    I worked out from my LMP (doctored slightly to adjust for early ov) I was due on 4th Feb, my 12 week scan put my EDD as 3rd Feb so that made perfect sense.

    Around 20 weeks I moved to a different area and changed hospitals, at 28 weeks I had a scan that dated me at 26th Jan. I discussed this with my consultant who said they would rather use their own dates and because it is only 8 days difference there is no risk of them delivering baby too early if they induce me 12 days over that date.

    However this new date means I would have had to have conceived during my last period so makes no sense at all. I am not concerned, its only a few days out but I understand at 8/6 weeks 2 weeks makes a LOT of difference to you. You must be really peeved to have gone from 8 weeks to 6 weeks, I was so excited to jump from 35 to 36 weeks, I would have been gutted if they moved me in the opposite direction!!

    Presumably you are having another scan at 12 weeks? I would wait until then and it should correct itself to a more accurate date as I said baby grows at a very predictable rate then and millimetres of difference can date you very accurately.

    Sorry you are so frustrated by your scan and good luck for the next one!!

    Miss I
  • i had an early scan at 5+4 and the consultant said i was pregnant and about 4-5 weeks. i said i thought i should be 5+4 (i did ov sticks!) and he said that looks about right. i had my next scan at 8+4 and they dated me as 8+4 too, so spot on. i had a scan at 12+2 and they dated me as 12+4. i know this one isnt right, and the 8 week one is correct as i know when i ov'd. nobody mentioned dates at my 20 week scan and there is nothing in my notes!
  • Hi,

    Early scans are not a good guide for dates so wait till your 12 week scans... from my LMP i was due 13th june, and early scan said 19th june another early scan said 23rd june and judging from baby at my 12 week scan (which is the one they will go by) I am due on 18th june...

    so jsut take it with a pinch of salt and be reassured that baby is ok in there - I think that's really the only thing early scans are good for XX
  • I won't get a 12 week scan as my first scan was an NHS routine scan that put me at 10+2 and my EDD is now all over my notes... But I am convinced it's a week out and that I am a week further on, but hey ho! And plus I'm now 18+3 so too late for a 12 week scan here, but good luck resolving your mysetery Fairythalia!!!
  • too be truthful i don't think scans produce accurate dates anyway, i had a scan at 9 wks which actually came to the conclusion i was 7, then another, 4 weeks later which put me at 12+6, and then at my 20 week scan if they went on babies belly measurement that would put me a week ahead, but if they based it on femur length that would've knocked me back 4, i hope that makes sense. i have always thought i was 4 weeks ahead of my dates due to me not having a period on the date they reckon my last one was. my belly is currently measuring 5 weeks ahead of my dates, so i dont know what to think, my current due date is 23rd april, which puts me at 25+5, but i'm on a quest to get everything ready by end of feb just in case.

    have got another scan on 5th feb (baby growth scan as i have small babies, which after 3 i would've thought they come to the conclusion that they are just born small and nothing can be done to help it), will let you know what those measurements say!!!

    so so confusing, why they like to confuse us is beyond me, rather than edd they should give a few weeks span as they say a normal pregnancy lasts between 37 and 42 weeks, not exactly 40!!!
  • Thanks for all your feedback girls. It's helped a lot and I feel tonnes better.

    I know it seems like I'm getting my knickers in a twist for nothing, but it just bugged me that they didn't say..

    Your date is roughly bla, bla, bla. but take this with a pinch of salt until week 12 scan (or something to that effect!)

    I think they forget that pregnant ladies are very particular about dates, especially if you were TTC for a while.

    I've been mapping and charting, ov sticks, temp charts for last 13 cycles; I think I know when my window of conception was.

    In the grand scheme of things I know it's not that big a deal and baby will come when it wants to regardless of date predictions but all the same... Grrrrr! :lol:

  • My cycle was VERY VERY regular and I know almost exactly when I conceived so have stuck to my EDD based on those calculations. All my scans show that the baby is 1-2 weeks ahead of schedule for all his measurements but if they change my dates it would mean I had conceived in the middle of my last AF! which clearly isn't possible. My husband is 6'4 so it looks like I am having a bigger than average boy image

    The first scan its so hard for them to measure accurately, so I would stick to your gut at this stage.
  • iam confused about scan dates coz both of them are either 2weeks ahead or 2weeks late,1 st one was due on 20.10.12 showed 11weeks 3days,on 29.10.12 it showed 12weeks 4days,now my lmp was 7.08.12 and i only had intercourse on 19.07.12 then again on 16.08.12,am confused please help me,what should i believe,going mad with my scans and dates of intercourse

  • You got pregnant on 16th August. 1st scan works out 2 days ahead as you were 9 wks1day from conception (they add 2 weeks on to the ultrasound date to date from first day of lmp) Stupid rule I know but it means you're not actually pregnant for the first 2 weeks of pregnancy. People with normal 28 day cycles usually ovulate on day 14 of their cycle so this would be the day of conception. Based on your first day of lmp being the 7th aug you ovulated 5 days early on 9th day of your cycle.

    With all this in mind your 2nd scan dated you more accurately and dated you only 1 day ahead. Your baby is growing perfectly! image Oh and scans in first trimester are accurate within 3-5 days as all babies grow at same rate before 12 weeks. After that the dates can change due to their own growth potential. So if any later scans date differently it's because your baby is growing a bit bigger or smaller for its age. Good luck! image
  • My blood test said that im 4 to 5 weeks on the 1st of january then I went for my scan on  13-02-2013 said Iam about 9 w4 d EDD 14-09-2013 but I cant remember having a period in december how is this ?......can someone plz help me the lady at the hospi said that I got pregnant on 23 dec ??? And if you look at the blood test it will be in 08-12-2012

  • Hi Olivia, your due date is usually based upon the start date of your last period so in theory you would have had your period around 8th Dec, you would then normally fall pregnant within the week following your period (so roughly 15th-21st Dec give or take a few days depending on your cycle).  Counting 9mths+1wk from your period start date should see you arrive at your due date which would be 14th Sept 2013.  Due dates can move forward/backward at scans depending on baby's growth but you should be confident you will have a Sept 13 baby.

  • Wondered if anyone could help me please. My lmp was 30 05 13 ... Next one was due roughly 27.06.13 which is 28days but sometimes i go 24\26 anyway felt rather rubbish 4days before period and took a test came bak positive. Had an early scan today should be 5.4 weeks yet lady at scan says in 4.8weeks (didn't no how she worked out 4.8) have a scan again next week but left me worryed as said baby was visiable yet - ive had 8 m/c and finally pregnant again and now left worrying for a week as to if there will actually be a baby there next week...sorry for the essay .

  • sorry i ment wasn't visiable.

  • Hi i have a bit of a complication.

    My ex girlfriend has informed me that she is pregnant and that on the 7/7/13 her scan revealed she was 12 weeks and a day pregnant which dates back to 15/4/13.

    We split up on the 2/5/13 and had regular intercourse until this date. However when we split in anger she slept with someone on the 6/5/13. Baby is due 25/1/14.

    Can anyone give me an insight to what the likelyness is that the child is mine?
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