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Pregnancy

Talk about every stage of pregnancy, from early symptoms to preparing for birth.

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Original poster

Does it matter that my dating scan is wrong?

15 replies

Bluesunday · 21/04/2010 19:10

I had my NHS dating scan today, I am 12 weeks and 1 day. I know this for a fact. My scan said the baby is 12 weeks and 6 days though - impossible as DP was working away and we only did it once that month (sorry TMI)! So my EDD is now Oct 28th instead of Nov 2nd. Does this matter at all, 5 days difference? Or is it too early to be meaningful? Will they revise my EDD at my 20 week scan?
The reason I ask is that my other two babies were big - 10lb 8oz and 9lb - I was wondering if perhaps I was having another whopper.
Sorry if this is a stupid question.

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Original poster

Bluesunday · 21/04/2010 19:11

PS - I know the EDD is calculated by my LMP but I'm 100% sure on that too

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MyThumbsHaveGoneWeird · 21/04/2010 19:24

The only thing I can think of is that if you go over they may be itching to induce you sooner than you'd like. But I think you can refuse that.

Haliborange · 21/04/2010 19:28

Don't know about your other questions, but I imagine it might only matter towards the end of pregnancy if you were being asked to consent to induction at 8/10/14 days over. Otherwise I can't see it making any difference.

Original poster

Bluesunday · 21/04/2010 19:29

Well I'd rather be induced tbh because my first labour was hell, baby was just too big. When the scan showed a 9lb at 39 weeks I asked to be induced and had a wonderful delivery. If this one is going to be big as well I'd rather not go over my EDD - so maybe it's a good thing it's earlier now..? I don't know!

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largeginandtonic · 21/04/2010 19:30

Sperm can live for 3-4 days in the body before actually fertilizing the egg.

It could be that.

They probably would not change it at the 20 weeks scan. Early scans are much more accurate than later ones.

I wouldn't worry

moonstorm · 21/04/2010 19:52

Honestly, I don't know. I know when my LMP was, when I ovulated etc. but I have had 5 scans that disagree with me and agree with each other - putting me 4 days ahead. I know they can be up to 5/7 days out, but the fact that they all agree with each other is strange. If anyone know about this I'd also be interested! Sorry about slight hijack!

Original poster

Bluesunday · 21/04/2010 22:46

Hi Moonstorm, I understand how your dating scan can give you a later EDD - like largeginandtonic said, sperm can live for 3-4 days so it's quite possible to concieve for a few days after you've had sex. But how on earth can you be MORE pregnant than you KNOW you are? Because if I'm 12+6, I must have concieved this baby 5 days BEFORE I had sex, ha ha! Why can't they just take my word for it - I KNOW when I got pregnant because I was there when it happened, ha ha! I don't know if they date you by the development of the baby or by the size, because like I said, I have a history of big babies so maybe this one is just another big one? I'm not worrying about it, I just don't understand how the sonographer works it out...

OP posts:

kickassangel · 21/04/2010 22:55

well dd was ivf, we knew to the HOUR when fertilisation occurred

Dating scan never agreed with our dates - when i said she was IVF, it was this date, this time, you're 3 days out, they just said, oh yes, it's all based on averages.

Missus84 · 21/04/2010 22:58

Sonographer works it out on size - they just measure the baby. So yours is a little on the big side.

5 days either side they wouldn't change the EDD anyway.

CarGirl · 21/04/2010 23:00

Going on LMP assumes you have a 28 day cycle though so if you ovulated early or late then that can affect when you actually conceived ie not 14 days after your LMP

tjtheminx · 22/04/2010 03:55

On my first pg the dating scan put me back two weeks. Impossible as DH had been away on business. DS turned up bang on 38 weeks. ( punctual like his mommy!)

This pg has been dated 3 weeks behind. I am now 27 + 2 according to my obs but 30 +2 according to my own calculations. If that's correct I got a BFP a couple of days before I concieved!

It's damn confusing I'll tell you. I suppose though it only matters in the last weeks.

MumNWLondon · 22/04/2010 08:37

It doesn't matter babies come when they want... I had 2 EDDs with DS2 (born last week) 5 days apart (ie scan vs LMP) and he came before either of them - 2 days early based on LMP and 7 days early based on scan.

However if you are late and they are talking about inducing (and you'd prefer not to be induced) thats the time to discuss the due date again. Otherwise its not really that relevant.

moominmarvellous · 22/04/2010 09:43

This has happened to me too, except they are saying I am 3 WEEKS further on when I can't be as I had a 5 day period within that time.

DD1 was 2 weeks overdue and I was induced, so at that stage it will make a massive difference!

I've already had 2 scans due to bleeding, both confirmed all is well, but I have my official 12 week scan on 30th (I will be 16 weeks then according to their dates) I'm worried something will be wrong due to the bleeding and size discrepancy. I guess we'll have to see how things progress.

LooL00 · 22/04/2010 10:03

My community midwife changed my due date when I was about 25 weeks, she said she was doing it as she was worried that 'they' would be bothering me about induction too soon ( as i am over 40) and since the scan date was the later one she changed it to that.All she did was cross it out on the top of my notes and write a new one in.
If you're working and are going on maternity leave the due date can change things if you're unwell as if you take sick leave within a month of your due date you have to start your mat leave early.

legallyblond · 22/04/2010 10:49

My midwife told me last week that the new guidance is that if there are any discrepencies at all, they will go with the date shown by the dating scan, rather than when you think you ovulated, what your cycle days were etc. The guidance that used to say that 5 days either way and they wouldn't change your EDD is now out of date. Not all NHS trusts are fully up to date yet - but they should be!!!

Although you are convinced about when you did the deed, they must I think go with the sonographer's measurements. If you have big babies anyway, I suspect its no bad thing as the main thing it will affect is when they will induce you!

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