early scans&dating?

[beckie90]

Does anyone know if they are reliable for dating a pregnancy? Or will it most likely change? Had my early scan today should be 7+5 by lmp, but scan said around 6+5? Meaning I ovulated day 21 when I am never that late at ovulation, in last 6yr I've had 2 late periods and that was only by 2 days. I'm pretty sure that that month I was slightly late ovulating but not by 1 whole week. Also I have a tilted womb if that effects anything early on? I had a posative test cycle day 29 xx

you can ovulate that late and have a 28 day cycle!

I know I just never have before I get ov pain and its always day 14 but it was day 16 that month thats just y I'm sure I'm not a full week behind. But the 2/3 times I've had late ovulation it turns my cycle late by how much later I've ovulated which has only been 2/3 days late cause my lp is 14 days so if I ovulated late my cycle wudnt be 28 days in my case.

I have a tilted womb and early scan dates matched OV stick dates. You can ovulate twice in a cycle too!

I don't know if this has been superseded by later, better research. FWIW:

I once found a proper (published peer-reviewed, methodical) study comparing dating from scans with known days since conception (all IVF babies). Off top of my head the study found that at 11.5-13 weeks the dating was +/- 3 days accurate with 95% confidence. So as many of 5% of babies would still be incorrectly dated. That's if you think +/- 3 days is truly accurate enough, too.

And that was the most accurate the scans got; before or after that window (11.5-13 weeks) the dating from scans became more erroneous.

So yes your dating could easily change with later scan; or not. Only time will tell!

My 1st scan put me 5 days behind my actual dating scan with ds1 so I don't have much faith in this tbh if thats when I concieved then I was only 8 days po when I tested n used a normal test not sensative so I don't get it, well Sonographer said they can be around 5 days out. I'm using my date my mw gave me till I have my dating scan. And at my last scan 12 days ago she said around 6wks then

X post liljkk Thankyou that reassures me abit more, I suppose given my expirience with ds1 would put my confusion at rest but somehow it dusnt lol

I had a scan and was put as 5 + 5 which would have meant I'd tested positive before conception!!! 14 days later had another and was dated 9 weeks! The scanner said they get more accurate the further along you get until about 12 weeks then gender and rave differences etc can have an effect.

You may well have your dates changed again :-)