to expect that a 'dating' scan should actually give me a more precise due date than my LMP??

[mummypig]

My cycles are extremely irregular - in the last year they have ranged from 29 days to 62 days with the norm being something around 35 to 40. I also did a HCG test four weeks after my last period and it came up negative. The first positive test was just over five weeks after the period and that was a very faint line. All of which I filled in on the form before my 'dating' scan. I thought I might be about 8 weeks, the sonographer said from the crown-rump length the foetus measures 9 weeks.

So why oh why did they then print off a form saying 'EDD by scan' exactly the same as from my LMP, and under 'comments' put "CRL does not correspond to dates. We will date the pregnancy at the nuchal/dating scan at 11w to 13w6d"? .

If I had been certain of my conception date I could see why they would do this, but I thought the whole point of this 'dating' scan was to get an accurate date. It just seems like they are making a problem out of something normal - why say the foetus is small if it is just younger than expected from LMP? And why bother with this 'dating' scan if they were planning to do a scan between 10 and 14 weeks in any case? And surely it will affect the outcome of the nuchal translucency test if the calculations assume I am one week further on than I really am?

I'm not really bothered about it as I shall take the 9 weeks measurement as being the correct one, probably won't go for the next scan in any case, and I am booking a great independent midwife who I'm sure will be very unflustered about supposed 'measuring small for dates'. I just don't see why they should take the LMP as the best prediction of due date when the likelihood that I actually ovulated on day 14 is pretty low.

I should also add that I had early scans with both of my previous pregnancies, due to irregular periods, and the sonographers did base the due date on the measurements.

I thought they normally adjusted your dates in to what the scan showed, not the other way round !

8 weeks is early for a dating scan though isn't it? Mine was at 12 weeks.

Oh, just read the last line .

Perhaps protocols have changed or something. Or perhaps someone who actually knows about it might be along...

Sorry - burbling...

Sometimes babies are small for other reasons though, maybe they just want to be thorough?

I'd go for the next scan and then see what they say then.

I had four early scans at 6, 8+5, 9+6 and 10+6 but they didn't date it until I had one at 11+6 as they get a more accurate result at around 12 weeks.

I thought that the later on in pg you are, the less accurate a scan will be in terms of determining dates from size of baby/peanut... so it doesn't make sense to me that they would defer to a later scan date...

i don't understand scans at all though - with ds, I had no idea what my LMP was - I was just off the pill and hadn't had a 'normal' period, jsut a few days of spotting, before I found out I was pg. The notes on our scan were that ds was estimated to be 8 weeks, but bigger than average. WTF? Surely if they were taking his 'age' from his size, they would assume he WAS average and calculate the date based on that????

lordy. the craziness of the medical world.

Think you make a lot of sense in not paying too much attention to it, tbh

ignore my 1st sentence in that last post, I am obviously badly informed

I think goingfor3 is right, that's why dating scans are based at 12weeks, not the size of the fetus as such, but what it has and hasnt got iyswim.

Dates by scans are only 95% accurate and can be out by as much as 5 days either side.
Don't forget - babies are only born on the EDD 5% of the time - your baby will come anytime between 37 and 42 weeks - though even that it isn't written in stone, judging by some of the early births in my AN club!
EG my friend was originally given a date of 28th September from her LMP. Dating scan more or less agreed. By 20 week scan she was measuring big for dates and was given a revised date of the 19th. Her ds was born on the 13th!

So yes, YABU I'm afraid!