Adamant that my due date is wrong!

[Mam2Be]

Longed winded, really sorry but I think that my due date is out by almost 2 weeks! Firstly because I remember my period starting on the night of my work's Christmas party and I thought "arggh this is so typical!" so that was the 11th December 2009. Following that I used an ovulation calculator to predict when I would be most fertile which was the 22nd-27th December and I made sure I wore out my OH for most of that week! Which would mean an EDD of the 17th September and not the 28th September which I have been given. The 28th would mean my period started on the 22nd December which isn't right!

I'm aware that these things are not an exact science and EDD's are never really accurate anyway but now that my little man is measuring big for his dates and my measurements are coming back large for dates I can't help wondering it's because he's coming sooner than they think. Plus I have to go through the fuss of yet another GTT.

Has anyone else been in this position and did you actually go early?

you could have ovulated latein your cycle as only 30% of women acctualy ovulate when there supposed to. i got pregnant 2 days before my period with 1st so ovulated extremely late.
but the scans are not always accurate though.

You always start your period about 14 days after you ovulate (I think the range is something like 12-16 days). But the first part of your cycle is very variable between women and just between cycles. So unless you are properly charting your temps and using OPKs you cant really know when you ovulated. I did all that, so am sure to within a day or so when I ov'ed, and my 12 week scan put me ahead by a week. So the only thing I can think is that scans are not that accurate? maybe for you it was a combination of both. At least you will be prepared if baby comes early!

My sister's in a similar situation to you. She knows exactly when she conceived as it was one occasion, but the dates given to her would mean she was on her period then and had conceived later, but that's just not right. This puts her dates out by about 10 days and now they're wondering why her measurements are so high.
I think a woman knows her body better than anyone so just be prepared for an earlier arrival! Good luck.

If you don't know when you ovulated, you certainly can't second guess a dating scan. Presumably you did have a dating scan between 10 and 14 weeks? They're very accurate.

Dating scans are pretty accurate and it's not massively out. Do bare in mind conception can be as late as a week after unprotected sex as sperm can last for ages inside.

At least they haven't got your dates out the other way around - if they were saying you were due earlier than you think then they would be badgering you for induction, so hopefully this way nature will run it's course and you'll give birth before they start wanting to induce. - Just keep mentioning at all your appointments when you think your date is if they start talking about being big for dates etc.
good luck with the rest of your pregnancy

that's not true Claire

My mum said I was due on 17 December. The medical lot said 5 Feb (lord knows how). I was born at 1416 on 17 Dec. my mum looked quite small but probably because I was OP. I think if you know exactly when you BD'd and that it couldn't have been any other date then you're right. The date of your last period is less accurate.

I had two due dates for ds (13 months) the one I knew was right and the one given by a scan. It wasn't a problem, I just had to remain confident cause I didn't want to be induced at all let alone way too early. It was an extra pressure during the last week or so but they listened to me and gave me time to go into labour. I would just talk frankly with your ob, explain how you feel about this mix up.

I should mention I didn't have a scan until 20 weeks, so I missed the boat for a good accurate reading about this.

Your due date would be 17th September by LMP but as others have said if you've had a dating scan and that's the date they've given you then you could have ovulated later (not sure how ovulation calculators work so can't comment on that). The due date from your scan doesn't consider your LMP so isn't telling you that your period was later just that your baby is due later because of when you conceived.

I would say that having been induced due to an overdue baby the later your due date the better as your baby is more likely to come on its own! Growth scans later on aren't as accurate so although baby may be measuring big I wouldn't worry about that too much, you can always turn down the GTT if you feel it is pointless.

What's not true activate?

Dating scans are accurate to a few days either way.

Ovulation predictor kits only detect a surge. They don't actually tell you when you ouvlate. It's perfectly possible to have more than one surge per cycle and perfectly possible to have a surge without ovulating. Also the fact that sperm can survive for several days inside you can make a difference, meaning the day you have sex isn't necessarily the day you conceive.

It does make a difference if you are absolutely sure of when you conceived and you are worried about care not meeting needs or fighting induction.

But otherwise, you baby will come when it comes anyway.

Ask them how they worked out your due date. If you definitely came on on the 11/12/09 then it should be around the 18th, ask the how they work it out and tell them your worries.

NamedAfter are you sure that dating scans are right to a few days? Im the other way round to OP. Due today but the more I look at the supposed time of conception the more I think they have got my EDD wrong. As I got pg after one cycle off the pill I wonder how they can be so sure. I am now into 'overdue' territory when I dont think I am. Was about to start another thread when I saw this title and joined in (sorry to hijack OP!)

seashore how did you calculate the date you knew to be right vs the scan date you were given?

Dating scans are accurate as in the first trimester babies grow at fairly uniform rates. If you have your scan notes you will see measurements on them - usually a first trimester scan will give HC (head circumference) and sometimes also CRL (crown-rump length). These will be in mm and are pretty standard measurements from foetus to foetus at this stage - if you google "foetal growth charts" or HC, you will find lots of tables which show the average measurements at different stages. A 20 week scan will give additional measurements - usually BPD (diameter of head, which can be less accurate than HC if the baby's head is a bit flatter than usual) and FL (femur length - usually quite accurate). Again, you can find average measurements for these on the internet if you are interested. A second trimester scan is less accurate though as past about 14 weeks babies start to develop more at their own pace - by the second trimester a scan is accurate to within a fortnight, and by the third trimester only to within 3 weeks. But a first trimester one is pretty accurate so I would go off that.

It's worth bearing in mind that ovulation is very variable, and using an ovulation calculator only gives you the most likely time, not a definite date. Even if you did ovulate on that date, you could have implanted later than you think. I wouldn't be too concerned, but if there's doubt I'd always go off the scan.

Btw - advice to OP - agree that if they have got your EDD wrong and you think you will be early this just gives you time to plan to be ready for the earlier date you have in mind. ~Youve got nothing to lose by being ready. Although if you start maternity leave earlier than you want and then youre wrong that could be annoying for you.

interesting lurcherlover, do you know how accurate a first trimester scan is? I have also read that there is still quite a range of crown to rump length and the scan lady told me that's what they estimated the age from at the 12w scan. Just interested!

Ov predictor kits aren't that accurate but according to 'taking charge of your fertility' if you chart as that book suggests (which is way more than just OPKs) it is pretty accurate to within a day or two. There was a thread on here somewhere about scan dates being out, lots of women who charted said scans were up to a week or so different. So I dont know which is more accurate? I suppose both could be out by a few days?

Taking Charge Of Your Fertility is an excellent book. I think it's 5 days either way for a first trimester scan which is pretty damn accurate imo. Mine was bang on (and I know when I conceived, was charting at the time and I know when I ovulate anyway as it fricking hurts!)

claire196 I believe crown-rump length is not quite as accurate as head circumference, only because some babies "hunch" their heads into their chests more than others which can make them seem shorter! Different hospitals have different policies in terms of what measurements they use. Even with crown-rump length in the first trimester they won't be out by more than a week max though. I would think that women whose scan dates differ from their ov dates implanted at a different time - it is impossible to know when you ovulated exactly (predictor kits detect the hormone surge, and ovulation can be 12-48 hours after that) and then also impossible to know when the embryo implanted - could've been three days later, could've been ten. So there are lots of variables even amongst women who know their cycles.

I think we probably get too hung up on EDD though - it's worth bearing in mind, that even in pregnancies where implantation is known to the day (eg IVF) the vast majority of babies arrive either early or late. In France, they give you a window of two dates, four weeks apart, and tell you to expect the baby at some point in between those dates! That seems much more logical really...

claire

"You always start your period about 14 days after you ovulate (I think the range is something like 12-16 days)"

this bit is not true - the 14 days is a statistical average and 12 and 16 are not true parameters but modal parameters ie cutting off the extremes of the bell curve

Agree. Says someone with a luteal phase of 9-11 days who is currently pg.

I stand corrected - sorry. My point though was really just that the luteal phase is much less variable than the follicular phase.

lurcherlover thanks for the interesting info. The french system does seem to make a lot more sense!

This happened to me. I KNEW when I had conceived and therefore due on 20th August. , but midwives and scan all said I was due on 3rd September.

Arguing made no difference, and I was annpoyed becuase it meant that my maternity leave would start later and that if I went overdue I was worried that there would be problems with my baby as I would be 4 weeks over, not 2 before they'd induce me.

Anyway, waters broke on 31st august and dd born on 1st september. To me this proves I was right as first babies never arrive on time or early. Medics say they were right

Nothing I'd ever bother myself about again, but at the time I got into a real tizz

My firstborn was 2 weeks early.