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Can a dating scan be inaccurate?

(14 Posts)
HuggleBuggleBear Mon 02-Sep-13 15:14:45

I had a dating scan in august and was dated 5 days further on than I thought. I did an ovulation test so know exactly when I ovulated although can these be wrong?

I did get a positive pregnancy test (very very faint line) at 10 days post ovulation test.

And 4 days after supposed ovulation I had a blocked nose which is always my early sign of pregnancy.

I guess my question is which is more likely to be inaccurate, the dating scan or ovulation test?

My due date is 15th feb 2014
Positive ovulation test 30th may
LMP was 13th may

This does not matter in the grand scheme of things but if my pregnancy is calculated further on than it is I might end up been induced due to dates which I don't want.

Thanks in advance

GreatJoanUmber Mon 02-Sep-13 15:29:41

Dating scans are inaccurate. They sometimes even change the EDD for ladies who have had IVF and know exactly how far along they are!
Trust your own body, and if you go overdue, fight your corner. Don't let them induce you just because you're too overdue by the dating scan dates.

Misty9 Mon 02-Sep-13 15:29:54

I definitely think dating scans can be wrong. With my first I knew exactly when he'd been conceived you don't forget one shag in four months! but scan put me forward by 4 days. My waters broke 4 days after supposed due date, though was still induced due to nothing happening fast enough.

Pregnant again and will take scan due date with pinch of salt smile

HuggleBuggleBear Mon 02-Sep-13 15:49:09

Thanks for your replies. I do think my dates are right and the dating scan wrong. I was induced in my last pregnancy after waters going and no contractions and went to 40+12 so every chance I'll go over again.

princesscupcakemummyb Mon 02-Sep-13 16:14:38

HuggleBuggleBear i think their not that accurate tbh i had my lmp jan 16th by that they gave me 23rd october then at the scan changed it to 2nd november im by their dates 31+2 its all guess work

comfyonesie2 Mon 02-Sep-13 16:36:31

Hi, I'm in exactly the same position as you - dated 5 days ahead but know exactly when I ov'd. I'm due on 9th Feb according to the scan, but am looking on the positive side as it means I can start maternity leave 5 days earlier grin. I went 9 days 'over' with my first, but I think the dates were wrong then too, so i understand where you're coming from. In my area, if you go over your due date by a long way (I think 42 weeks) you are offered daily scans to check all is well - I'd do that rather than have another induction any day!

eurochick Mon 02-Sep-13 16:41:37

I agree with GreatJoan. I've heard of IVFers arguing with drs who are telling them that conception happened at some time other than the 24hrs in which they absolutely know that sperm and egg met!

HuggleBuggleBear Mon 02-Sep-13 17:21:49

I'm glad others have had the same experience or heard about people who have. When I had my dating scan and calculated it i realised it didn't make sense but its difficult because the date they give u is what they go by and u dont want to say its wrong. I will be doing everything I can to avoid induction this time round.

impecuniousmarmoset Mon 02-Sep-13 17:25:22

The thing is, implantation can take variable amounts of time after ovulation, so even with IVF there could well be some discrepancy between where you think you are and where you are on the scan. Not to say scan is necessarily right, but within a margin of a few days I'm not sure it's possible to say that they are definitely wrong and you are definitely right.

CrispyFB Mon 02-Sep-13 17:52:47

Usually before 10 weeks they're accurate to within 5 days most of the time. Embryos follow a pretty set path before they are fully formed and start the business of "just" growing. The earlier they are (so long as there's something to see..!) the more accurate they are.

After the baby has fully formed, bets are off.

All my babies have measured within 3 days of my (charted) ovulation dates up to 10 weeks, in most cases spot on or 1 day out. And I've had at least 2-3 pre 9 weeks scans per baby due to the joys of spotting and bleeding.

Yet they all measure 4-6 days ahead by 12 weeks! Most dating scans seem to be done post 10 weeks on the NHS which seems odd as it's less accurate then.

GreatJoanUmber Mon 02-Sep-13 18:07:07

impecunious while it is right that implantation may occur a bit later, that would mean it gives you a later due date.
However for them to say you conceived a week before you actually did makes no sense in most cases; especially those with IVF involved!
FWIW, apparently I conceived my DS2 one day after my period ended and before DH and I had sex that cycle. Go figure...

HuggleBuggleBear Mon 02-Sep-13 18:19:49

That's interesting about earlier scans been more accurate in my last pregnancy I had an early scan then had a dating scan and they pushed me 3 days further forward at the second scan. I feel better knowing this now as it makes sense that babies grow at different rates

HopeS01 Mon 02-Sep-13 19:49:27

Hi ladies,
Same here. I'm 100% sure that my DD is at least 5 days late... At my 12 week scan they moved the conception date back by 7 days. I'm going to ask them to have another look at my 20 wk scan (in 2 weeks). The new conception date they have given me is 5 days into a work trip in Italy (where I certainly didn't conceive!) Also, if the date they have given me is correct (which is impossible) it would meant that I got a very clear line positive result on a home pregnancy testing kit at 3 weeks (I thought I was 4)
Anyway, I'm sure he or she will born whenever they please but as I'm so sure the date is wrong it's worth mentioning, right?

smile

flowersinavase Tue 03-Sep-13 04:57:22

A scan is only as accurate as the person doing it and the equipment they use. We're talking millimetres here so if you had the scan done ten minutes later by someone else you'd likely get a slightly different result.

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