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Wrong scan dates??

(9 Posts)
BellaBells Sat 06-Aug-11 23:13:40

My EDD was 19th September, this was estimated by scan as I could not remember my LMP. I went for a private scan firstly for reassurance and I had worked out I should be about 8-9weeks, however I was told I was about 6 weeks (this was again taken purely from scan measurements). My 12 week scan and 20 week scan gave me different EDD but was told to use the 20 week date of 19th sep. So I have up to now gone by that which puts me at 33+ 5. BUT I had another scan yesterday and with all the measurements etc I was told DS is measuring at 36 weeks and he also weighs in at 36 weeks. Can this happen?!

janey223 Sat 06-Aug-11 23:56:14

Jeeze, I couldn't cope with that!

Sorry, not much good but hopefully they're right this time, eek!

CollieandPup Sun 07-Aug-11 01:18:39

I'm surprised they went with your dd from your early private scan as I went for one at 10 wks which was slightly different to the nhs one at 13wks and they wouldn't use the private one, even though on the day of the nhs scan she struggled to get the measurements.

Dates from early scans are also nutritiously inaccurate as apparently growth early on can vary so much so it sounds to me like the dates from your early scan where out....I'm assuming the later scans at 12 and 20 wks dated you further on?

Your mw has the ability to change your dates. I'd speak to her. 2 weeks is a big deal especially if you go over and they won't induce you.

nannyl Sun 07-Aug-11 09:48:19

Could you just have a big baby?

I have no idea btw just wondering?

I am sure of my dates, and i have a big bump (which has always measured big) but a "normal size" baby inside (apparently)... im 35 weeks today

Mum2be79 Sun 07-Aug-11 10:05:54

My mum knew her date of her LMP and when she went for her first scan, she was told I was due on December 24th, even though her dates were putting it at January 22nd. Then further on, she went for another scan (apparently she wasn't growing much) and they said mid-March!!!!!! My mum replied that she must be an elephant. She was told to go with her dates but then on January 1st, it was thought I was going to make an appearance but I was just lying on a nerve.
I was born one week after my mum's dates.

The moral: Go with your own dates. Whereas scans be be close to accurate, they are not 100% as my mum found out with me. Granted it was 1979 but it seems I may be going the same way - rapid growth in the first half and then showing signs of 'slowing down' probably until the 8th month like my mum and my aunt.

Tangle Sun 07-Aug-11 10:38:09

Scans at any point can lead to inaccurate dates.

If you scan early, you're trying to measure something that's so small that any error in the measurement (no matter how small) will lead to a significant discrepancy in date. On the plus side, the latest research I know of shows that babies grow at a fairly uniform rate up till about 8 weeks, so if you can get an accurate measurement at least there isn't too much range on the date.

At 12 weeks you're still looking at something pretty tiny, and any given crown-rump length now has an error margin of +/- 1 week.

The alter you get in pregnancy the bigger the baby (so measurement errors are less significant as a proportion of the measurement) - but the more discrepancy you'd expect in the size of a baby at any given gestation.

And on any of those, you're trying to measure something that is 3D and mobile and you're trying to do it remotely - using a technology that isn't 100% perfect operated by someone who is highly trained, but still human...

If it were me I'd probably work off one of the early dates for myself, and try and ignore the later ones. The problem that you may run into is if your local PCT has a policy of recommending induction at 41 weeks (or thereabouts) - you may not wish to accept that recommendation purely on the back of an EDD calculated from a scan performed post 30 weeks, especially when you had earlier scans giving you a later EDD, but you might find yourself under considerable pressure from your HCP's to do so.

catsareevil Sun 07-Aug-11 11:11:27

Its highly possible that a baby later on in pregnancy can vary in size. What was the date on your 12 week scan - that would usually be the most accurate time to date.

BellaBells Sun 07-Aug-11 11:33:14

I was given the most recent scan on 05/08/11 because I started to go into labour just over a week ago, at what we thought was 32 weeks. They managed to stop the contractions but they performed a scan to make sure all was well. They measured the abdomen, head circumference, femur length etc and he was on par with now 36 weeks +1. They also wrote that on the scan report; gestational age: 36 weeks +1 day, est fetal weight: 6lbs 5 ozs.

I know you can of course get big babies but do all of their measurements ;head circumference, femur length, abdominal circumference etc, measure larger too? And the weight? My dr read the report and didn't say anything, probably because it says that everything is within normal limits for 36 weeks?!

So sorry ladies if this isn't making much sense! I am just slightly more paranoid because if I am 36 weeks I might change my thinking that the contractions I'm having aren't BH but could be labour starting up again! The 36 weeks puts me about where I thought I should have been if I try to work out my LMP.

galwaygal Sun 07-Aug-11 17:28:45

If you have a tilted uterus your early scans can measure up to 2 weeks behind. This corrects itself when the uterus rises above the pelvic brim at around 12 weeks.

The most accurate time to date a pregnancy is around 12 to 14 weeks, when the error is approx +/- a week.

After this time the measurements can be way out again, dependant on growth of baby.

So if your 12 week and 20 week scans agreed on a date, then take this date.

Later scans are definitely not accurate, just do a search through threads on mn of baby small for dates or big for dates to get reasurrance that later scans do not accurately predict big or small babies and can be wildly out on size and weight of baby.

Ideally do take the date given by your 12 week scan, but be aware of the week variation on accuracy. HTH

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