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Are due dates from scan always accurate?

(15 Posts)
Hormoneoverload Sun 26-Jun-11 21:32:44

Three days overdue according to scan dates here, but according to when I ovulated and must have conceived, two days to go. I'm so not convinced by the date given by the 20 week scan and know it might become important in a few days time if induction being discussed. Any wisdom? I fully admit to seeing sonography as a dark art that I really don't understand!

NoWayNoHow Sun 26-Jun-11 21:36:20

My EDD before my first scan was 3rd Nov, but when I went to the scan they told me I was about a week out and was actually due 27th Oct.

Roll forward 25 weeks and there I am with a "big baby" according to MW as well as excess water, and apparently no chance whatsoever of going overdue.

27th Oct comes. And goes.

DS born on 2nd Nov! Personally I reckon because he was a big baby that my original due date was right, and that his size threw the sonographer off at the scan.

JentlyDoesIt Sun 26-Jun-11 21:39:03

My edd with ds wasn't actually decided on until I was in the delivery room! It was decided his edd was 22nd November, he arrived on 1st November at a v healthy 7lb 15oz!

I was on clomid so dates were pretty certain smile

Ilovekittyelise Sun 26-Jun-11 21:41:02

your dates are correct if you know when you ovulated; scan dates are based on averages and your baby being slap bang in the middle of a growth curve, and get progressively less accurate (the most accurate being if you have a super early scan at around 6 or 7 weeks when foetuses vary less in length).

i had a scan an 6+3 which was correct (knew when i ovulated) then at the next scan the dates were pushed forward 5 days, i had to argue my dates to get them agreed as those i knew were correct, because due to a pre-existing health condition im already under pressure for early induction...

let us know how you get on, im really interested to know the timeliness of labours from people who know for a fact when they ovulated and hence are actually due!

Hormoneoverload Sun 26-Jun-11 21:48:33

Very helpful. Tuesday is my due date from lmp, ovulation date and six week scan. So I will be sticking to that as far as induction is concerned. I'd like a home birth if no reason to go anywhere, would never argue for one against medical advice, but certainly don't want to be induced on dates that I don't trust. I guess if I'm offered a sweep on tues based on being nearly a week overdue I might change my tune wink

nannyl Sun 26-Jun-11 22:32:54

Mine is 2 days out.

I have charted for months and know exactly when i ovulated.

However when discussing this with the sonographer she was telling me that the dates they give (at 12 weeks) are accurate to + - 5 days. (therefore the hospital is sort of agreeing with my date, as it IS still within + - 5 days)

I think the smaller it is the more accurate the dating is, and as time goes on its not quite so accurate anymore

dowelly2k Sun 26-Jun-11 22:45:08

The doctors and sonographers couldnt agree with my pregnancy even though I knew when I ovulated. One doc said it was the 23rd April, the next said it was 17th April. In the end my son was born on 22nd April and I knew he was overdue as his skin was dry and cracked around his wrists and ankles.

CBear6 Sun 26-Jun-11 23:24:05

With DS the MW estimated 10th July based on LMP which I was sure was incorrect. 12 week scan showed a little blob, was rescanned six weeks later and was told I was 13 weeks and DS was due 23rd August. He measured big all the way through the pregnancy and eventually arrived on 23rd August - slap bang on time according to the scan and weighing 9lb 3oz however he still had some lanugo hair and the delivery MW reckoned my due date was out slightly and he was actually a little bit early! If that's true then I dread to think how much he'd have weighed if he was on time or overdue.

With this one the MW estimated 20th August. I knew when I'd been at it and when I hadn't and that I'd been having a regular six week cycle since a mmc earlier in the year (she based her dates on a four week cycle). I estimated 15th September. Scan showed 11th September, DH is convinced she's coming on the 10th but I'm putting my money on the 15th.

I was told that scans can be out by up to two weeks!

shelsco Sun 26-Jun-11 23:37:40

My scan date was about a week and a half earlier than my dates (which I was pretty sure about). When ds was born I was 3 days late according to scan date but early according to my dates. Mw said when I gave birth that there was no way that ds was a late baby as he was still absolutely covered with that stuff (can't remember the name- vernix or something?) that babies have when they're early.

emsies Sun 26-Jun-11 23:50:08

Do remember that gestation dates vary too - so any time from 38 weeks until 42 is still within bounds, ie 2 weeks after "due" date is still within the due period. You're not actually late or overdue until 42 weeks.

Hormoneoverload Mon 27-Jun-11 05:56:20

Thanks! I won't do anything about it now, but in my head I'm not overdue any more and will use tues as my date if induction comes up at any point. The docs in hospital when I was in fir five days with unstable lie worked hard to avoid intervention and I don't want to be induced without sound reason, although have no objection if it's necessary.

exoticfruits Mon 27-Jun-11 06:05:54

It wasn't accurate in my case. In the end they agreed with my dates which were much earlier.

babyonbord Mon 27-Jun-11 11:31:47

due dates are a rough indicator they are not meant to be taken literal. I don't know a single person who has actually given birth on their due date unless it was a planned c section or they were induced. You are technically due any time in that 5 week period beginning at 37 weeks, so there is a lot of leeway, scans are as accurate a measure of when you will go into labour as you can get as it is based on your babies growth and development.

saoirse86 Mon 27-Jun-11 13:08:12

I had my first scan at 16+3 (clearly I didn't know what my idea of an EDD was!) and my due date was 24th september. They were absolutely right! She was born on that day weighing 6lb 14oz.

My sister's due date was 18th september (although she thought it was 13th IIRC) and she was born by emcs on 17th september. We reckon if they hadn't intervened she would've come on the 18th.

KaraJS Mon 27-Jun-11 14:46:23

Don't think mine were right, when my waters broke at 31 weeks baby was measuring 33+4 he was born at 32 weeks but neonatal thought he was a couple of weeks more due to how well he was feeding, they did tests and decided he was 34-35 weeks, sometimes in the beginning u can have bleeding that you just think is a period

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