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Confused - Ultrasound showing 12 weeks pg and its not possible!

(8 Posts)
kurlyvoice Thu 28-Feb-13 10:57:03

I've had it with both of my pregnancies - I think because they're doing it on head circumference and our family all have enormous heads. They dated DS as a week further on that I knew we were, which was a bit of a problem when he arrived early because of preeclampsia and I knew he was 34 weeks but the notes read 35. This pregnancy, I am 40 weeks today by scan dates but I know by ovulation tracking that I'm actually 39+2. At this stage I'm not complaining as I have horrendous SPD and want baby out ASAP!

BraveLilBear Thu 28-Feb-13 10:40:47

Hi Cookie I had this too...

I know exactly when I conceived because I always experience ovulation pains, which normally is almost exactly 2 weeks before first day of AF. When I had my 12 week scan, I would have been 11+3 if I conceived at the moment of ovulation (late in the evening on that day), or a little less if it took a while for the bits to meet up - which seems more likely.

They measured me at 12+2 - at one point it said 12+5 on screen - but after she'd remeasured she said 12+2.

The annoying thing is that everyone keeps saying 'oh but that matches exactly with your LMP'. It does, but, it was an early miscarriage and it took me 4 days to get BFN afterwards (therefore I ovulated about 4 days late) - plus I have a starting cycle base of 31-32 days, neither of which has been taken into account.

There was some reassurance when I saw that the scan was +/- 5 days accuracy (tho not a whole week!) and have spoken to mw about the fact that I don't want to be pushed towards an induction earlier than 'my' dates (unless there's a medical need, of course) and she said that no-one would make me have an induction if I didn't one, and that they should listen to me when the time comes.

Anyway... you're not the only one!

Cookiepants Wed 27-Feb-13 22:32:08

Thanks all, feeling much better now x

Havingkittens Wed 27-Feb-13 21:31:31

Yes, very possible. They date according to size at that stage rather than exact gestation. I had fertility treatment too so know exactly when I conceived but had regular scans from very early on and measured between a day and 3 days ahead at 3 different scans so if I'd have had my first scan at 12wks I would've been surprised to find I was 5 days ahead of what I should be.

Spinaroo Wed 27-Feb-13 21:28:48

A scan of 12 weeks means you conceived roughly 10 weeks ago. Testing at the time you sat you would have been four weeks is actually only a couple if weeks after conception. If you test a day too early it might not have shown uo

Cookiepants Wed 27-Feb-13 21:24:11

Thanks Elly, I wasn't actually having periods which is why I was so focused on the scan! Last period was nearly 8 months ago. I suppose it could have been a duff test / user error. Just quite puzzled is all. X

Ellypoo Wed 27-Feb-13 21:08:11

An early bfn is perfectly possible - some tests aren't as sensitive as others.
They date your pg from the 1st day of your lmp roughly 2 wks before conception would have actually occurred - are you building this into your dates?

Cookiepants Wed 27-Feb-13 20:27:58

Hope someone can advise me. Had dating scan today which showed I am 12 + 3 weeks along however I'm not sure how that's possible as I needed fertility treatment to ovulate which I didn't start til the week AFTER I would have conceived confused. Has anyone had an ultrasound showing they were further along than they thought they could be? I also did a pg test when I would have been 4 weeks according to scan which was BFN. Any advice would be gratefully received!

TIA thanks

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