'Pregnancies vary by 5 weeks'

Has anyone read this article on BBC today?


Whilst I don't think I25 people are enough for the study, it is interesting and something I agree with. I've been moved forward by 6 and 4 days in my pregnancies from when I know I ov'd and am always suspicious of how many people truly go 2 weeks over their true EDD.

I think it would be much better to give people a due window rather than a due date.



  • I definitely agree it should be a window, not a day. There is so much variation.

    I was moved too even though i was temping and so sure of ovulation. Thing is day of ovulation can vary, as can day of conception ie it can be day of or day after ovulation. Time to implantation can also have an effect. So many variables which it's impossible to pinpoint.

    I guess though everyone knows that duedates are a guidline and you can refuse induction if you are overdue but not by as much as they've told you you are.

    What's always interested me is what do they use to move you dates at 12 week scan? Is it average size for that date? Surely that works on the basis all babies should be the same at 12+4 or 13+1 or whenever you have your scan.

  • I was moved forward 4 days with my first 2 which wasn't even possible as A was IUI so by their dates I conceived before I even had the IUI. Suited me though as it meant I got induced earlier, and with J I got a sweep earlier which put me into labour

    AR - I'm sure they date you using the crown rump length at 12 week scan so if you're bigger is bigger or smaller than average it will change your dates

  • Thats what i guessed. SO you could be moved back when in fact baby is just below average size wise? I'm not sure how varied thesize is atthis stage. I was moved forward over a week at 12 weeks,despite being sure of dates. And then she measured small at 20 weeks, i did point out the change in dates to the sonographer but she wasn't interested.

  • It probably figured that Ally and I were moved forward and had big babies.

    I had to really fight the mw first time round to have my dates noted on my file, my worry was being pressured into induction at +8 rather than +14. I even had cd21 blood test results which meant I couldn't have possibly conceived when they said I had.

    I guess the question is how else are they supposed to measure, most people don't know when they ov, and as you say AR, even less when implantation takes place. I just don't think the one size fits all method used at present is particularly helpful when most people are induced by +14. Very few people refuse induction, partly because they've spent 8 months looking forward to one day and so by the time they go 2 weeks over this arbitrary date are desperate to get the baby out.

  • I don't think size varies that much at 12 weeks though. I had 2 big babies and at my 20 week scan 3rd time round I commented on how all the measurements were coming up at being 20+1 roughly so maybe I wouldn't have a big baby this time. The sonographer said that it isn't until a bit later that babies start their growth spurts or their growth slows down and that up until then they should measure around the same

  • Last time I thought they dated me early by 4/5 days by my calculations. By them he was due on 1st (I thought 4/5th) and he was born on 9th. This time... Well, I think they put me back by 3 days I think. Although I am not sure whether I would agree or not or have 'a feeling' on when this one should be due. My ELCS is as close to due date as they would let me go, so hopefully that means baby is as ready as they should be? Am terrified of earlier labour as I have too much I need to do as it is!

    I'm 37+4 today anyway,so technically would still be term if it came now

  • I went 17 days over and love the idea of it being more flexible. I understand there has to be 'a date' for records and employment etc, but surely every pregnancy should be judged on its own merits and dealt with accordingly?

  • They have tried to pull my dates forward this time - by 4/5 days. There is no way i ovulated 16days after a miscarriage started. I normally OV on day 20/21 of a cycle. Plus it would also mean immaculate conception! I think i cook bigger babies -bigger at 12week dating scan and thus dates are brought forward. Making due dates a nonsense really! Makes me wonder if they did the same with first baby - meaning she wasn't as "late" as she appeared to be.

  • I agree there's probably less variance at 12 weeks than, say, 30 weeks but there must be some variance, and a mm here or there could easily make a difference of days or a week.  I know they try to induce by 40+14 because there is a higher risk of  still birth after then, but it seems a bit too 'one size fits all', I'm not sure what the solution is however. And expected due 'window' does seem to make sense, though old habits are hard to break, people would still take 40w as their due date.

    I remember reading an article ages ago that suggested the mode average pregnancy length is 41 weeks, but the mean is 40 weeks. So most people should expect to go a week over.

  • There is quite a lot of possible variance at 12 weeks, and they rigidly set the EDD based on the 50th percentile, while just isn't realistic.

    This research paper has an appendix at the end which has the difference sizes and gestation. www.bmus.org/.../23-17-3-161_ultBMUS.pdf

    I know exactly when I ovulated, and I had a scan at 8+1 and the embryo was measuring 19.9mm. They moved my dates forward to say I was 8+4 because that was 50th percentile - actually at that size, I could have been anywhere from 8+0 to 9+2. At my next scan, I was moved back 5 days, and then at the 3rd scan I was bought forward again 2 days to the dates I'd said all along!

    In France 41 weeks is counted as the EDD and they won't induced for being 'overdue' until 43 weeks.

  • I was moved back a week both times and had a huge first baby. They have moved me back a week this time too. I just hope this one is more an average size.

    I do like the idea of a due date window than a specific date.

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